Understanding Algae

And here is one great feature From Koi Guru Mike McMahnon on algae 

First off, this is not a thread about string algae 'problems'. As regulars know, I have an inordinate interest in algae. For years I've tried to develop an understanding of string algae in particular. I have read a great deal about it, but whenever I have thought I'd learned something giving insight, I'll read a study that contradicts what I thought I had learned. In fits and starts, I'll plough through articles that are largely incomprehensible trying to get to the root of what happens in our ponds. I'll grow frustrated, put it all aside as a waste of time and then return to it weeks or months later. Sometimes I think I'll never really grasp the subject. But, the challenge eventually draws me back.

It would be great to be able to write an article to share real knowledge. I have doubts that I'll ever reach that point. Still, I keep seeing threads on koi and pond forums giving contradictory advice, things being said that are only partially correct or are incomplete, and lots of chatter about folks resorting to all sorts of chemical weapons to combat string algae with little thought about the impacts on the pond eco-system. If I had the time, I'd be spending part of everyday replying to the multitude of things people say about string algae. I control myself most of the time, read what people say and move on. But, the superficiality bothers me, even though I have no great insight to reveal. So, I've decided to start this thread with the idea of having an on-going series of posts on different aspects of string algae, each something of a 'mini-chapter', if time and energy permit. As I learn that something I've posted is inaccurate, I hope to go back and edit the original post, or perhaps post an update. It is hard to say how many 'mini-chapters' there will be. The subject really has no limits to the side trails one can wander.

The Identity Challenge

Nutrients

Reproduction

Currents

Light

Temperature

Impacts on Water

Aellopathy

Diseases

Residents

Food For Koi??

Controlling String Algae

1. Limiting Light & Nutrient
2. Chemical Treatments: Hydrogen Peroxide
3. Chemical Treatments: Copper
4. Chemical Treatments: PP
5. Chemical Treatments: Others
6. Barley Straw
7. Clay & Kitty Litter
8. High Tech Gizmos
9. Plecostomus
10. Bacterial Additives
11. Bog Gardens
12. Other Chemicals
13  Algae Scrubbers 

The Identity Challenge

Most literature identifies our string algae as being in the genus Cladophora. When a species name is given, it is usually Cladophora glomerata. An identification problem immediately arises because science does not agree on how many species there are. One taxonomist says there are 5 known species, another will say there are a dozen or more. Within each species, there are forms or varieties, and the taxonomists differ on the validity of these differentiations. Adding to the confusion, algae identified in the wild will change form when grown in laboratory conditions. What appeared to be two different species, or two different forms of a single species, may become identical to the eye when grown in identical, controlled conditions. And, there have been instances of what seemed to be a single species in the wild differentiating when grown in identical conditions in the lab, revealing that there were actually two species co-habitating in the wild. However, some forms of a particular species will retain the differentiating traits in most conditions (although perhaps not in all), giving credence to the idea that there truly are different varieties within particular species marked by differing growth habits. Because the growth habit of string algae will vary according to numerous factors, including (but by no means limited to) nutrient availability, current, light intensity, co-habitant influences, temperature, stage of maturity and such, visual determination of a scientific identity can prove erroneous. It really takes an educated eye to be certain.

DNA analysis to differentiate species and forms has been utilized, resulting in debate as to how different DNA has to be to support a species identification, rather than differentiation between individuals. Some species have such significant DNA differences from other species that there is not much to debate. Some appear to be more gradations of differences, causing a challenging question of where to draw a line, and whether to draw a line, particularly when the differences at the extreme ends of the gradation range seem dramatic at first blush.

Adding to the complexity, analysis of antibodies produced by string alga (yes, algae produces antibodies), has shown such high immunological distances between certain species as to raise the question of whether all the alga classified as Cladophora rightfully belong in the same genus. One authority on alga taxonomy has described the identification issue as simply 'problematical'. When a scientist who has spent decades of continual taxonomic study so speaks, I am hardly going to venture a guess.

For the purposes of pondkeepers, we are likely correct if we say our string algae is Cladophora and not bother about species or forms. However, the fact that different species and forms do exist and mimic one another in appearance under certain conditions, is, I think, a major point to keep in mind. When a study finds string algae populations collapse at a temperature of 25C, and another finds them thriving until the temperature reaches 32C, the contradiction may not be a contradiction at all. Both may be accurate observations of different species, or different forms. But, do not jump to the conclusion that all is explained by different forms being involved in apparently inconsistent observations. There are numerous other factors beyond temperature that can play a role in population collapse.

So, for my first substantive post, I think the practical way to address identification of what is growing in our ponds is to just call it string algae.

...which I think well explains why I get frustrated in trying to learn about the stuff. I called it string algae before I spent all those hours reading about it

Nutrients

There are a number of nutrients that have been found crucial to the success of string algae. Nitrogen and phosphate are the ones of most focus, largely because these are waterway pollutants frequently studied. Other nutrients identified as crucial include silicon, boron, iron, zinc and B-vitamins. In particular conditions, there are undoubtedly others that would be limiting factors.

There is always a lot of comment about nitrate levels in ponds with a bloom of string algae. Studies show that ammonium is the preferred nitrogen source, not nitrate. The string alga are not efficient in using nitrate. However, the utilization of nitrate increases with higher levels of phosphate. Numerous studies indicate that phosphate is the nutrient most critical to a sudden bloom of string algae in natural waterbodies. Add phosphate and the algae proliferates. Limiting phosphorous, however, does not necessarily result in the die-off of the algae, at least not over a short term period. String algae come well-equipped to deal with phosphorous shortages. They take up a luxury amount of phosphorous when it is available. That is, the algae will store excess phosphorous and use it as ambient phosphorous levels in the water decline below what is needed for growth. String algae also possess an enzyme, phosphatase, which is thought to allow it to maximize the use of organic phosphorous available in the water. It would seem apparent that string algae evolved to take advantage of environments where nutrient availability fluctuated radically.

String algae did not evolve in isolation from other life forms. It is the host for numerous other organisms. These are referred to as epiphytes, organisms that use the algal filaments as a substrate. Of particular interest are various diatoms that colonize the surface of filaments. Some of these diatoms harbor photosynthetic bacteria (blue-green algae) that have the ability to fix atmospheric nitrogen. Atmospheric nitrogen is abundant in dissolved form in water, but cannot be used by plants to meet their nitrogen needs. I'm sure nearly everyone is familiar with the ability of the peanut plant to enrich the soil in which it is grown by adding organic nitrogen. This occurs in root nodules which house bacteria that produce nitrogen in useable form as a by-product of their metabolism. The diatoms colonizing the surface of algal filaments have this ability. A thriving epiphytic colony of diatoms bathes each algal filament with useable nitrogen. The water may have a very low level of available nitrogen, while the concentration at the molecular surface of the algal filament is quite high. The author of one study of a northern California river suggested that the production of useable nitrogen by the epiphytes borne by Cladophora made a greater contribution to the health and vitality of the aquatic plant communities of the river system than any other nitrogen source. Whether that was a bit of over-exuberance or not, it highlights an important point. String algae hosts organisms capable of supplying its nitrogen needs.

It seems logical that if one eliminates nitrogenous wastes from a pond the algae will die. But, I'm sure those who have borne with me this far have read of experiences where string algae was thriving despite very low levels of detectable nitrate and no detectable ammonia or nitrite. We cannot know the reasons in any particular instance. One possibility is that the string algae community of organisms is simply producing all the nitrogen it needs to supplement the undetectable traces of ammonium continuously produced by the fish in the pond. Every time food is added, phosphorous is added, and the string algae take in all they can to use and store for future use. The two nutrients most examined are both ones that string algae has evolved to take care of for itself, at least to a sufficient degree that survival chances in low nutrient environments are rather good.

The adaptations of string algae to the low nutrient environment of natural streams make the abundant nutrient environment of the koi pond heavenly. So, why doesn't it exhibit overgrowth all year round in every pond? Once again, nothing about string algae is simple.

Reproduction

String algae has a complex reproductive strategy. The simplest means of reproduction has been observed by every pondkeeper. Filaments that break off will become lodged on any rough surface or obstruction and continue growing. The rhizoid-like holdfasts that anchor it to a surface are not necessary for growth. Pinch some off the wall of your pond and you likely have hundreds of filaments in your fingers, each capable of colonizing new territory. Have you ever thought about how many filaments there must in your pond during a bloom? Millions? Trillions? It really is beyond comprehension. However, as numerous as all those filaments may be for successful vegetative reproduction, it is nothing compared to the other weapons in string algae's arsenal.

Cladophora has a type of sexual reproductive strategy similar to mosses. It is diplohaplontic, meaning that it follows a two-stage process. The mature plant produces spores. The spores become gametophytes, a stage of growth capable of producing gametes, cells with only half of the chromasomes necessary for a complete organism. You might think of these as eggs and sperm, but they are not really either. Two gametes will merge, forming a new plant. The new plant may arise from the gametes of two different parents or the gametes of the same parent. In mosses, the gametophyte stage of growth is physically different than the appearance of the mature moss plant. In Cladophora, the gametophyte state looks the same, or at least enough so that pondkeepers are not going to tell the difference. Not every species has been studied enough to confirm that all are diplohaplontic, but none that have been studied have been found not to be. Each filament is capable of producing an uncountable number of spores.

String algae also produces zoospores, which you can think of as living baby plants. (This a misnomer, but helpful to understanding, even if not really accurate.) It is this means of reproduction that hobbyists observe all the time without realizing it. As filaments mature, zoospores form within the cells. When mature, the growing zoospores cause the cell wall to rupture, releasing numerous zoospores into the water. The zoospores of Cladophora have flagellae which are used to swim through the water at what is a rapid speed for the little organisms. (Scientists refer to them as protoplasts, rather than organisms.) Within a short time, probably not more than a couple of hours, the zoospores come to rest on the surface of some object in the waterbody, such as the pond wall. There they secrete cellulose, forming a tough outer cell wall and begin developing holdfasts, effectively cementing themselves to the surface each has claimed as a new home. They then begin growing the long filaments we think of as string algae. When the zoospores cause the parent plant's cell wall to rupture, the damage is permanent. The rupture releases cell matter into the water and allows bacterial invaders to begin the decomposition process. This is what we see occurring when we observe a die-off of string algae. Since much of the algae matures at the same time, the die-back can be dramatic over the course of a few days or weeks. It is a common observation that as a die-back occurs, the strands of algae clump, an effect of the gelatinous cell matter of innumerable ruptured cells sticking together; and the water takes on that algae smell we all so dislike. We may be pleased that the trillions of filaments are in dramatic decline, but we do not notice that every filament in decline has released thousands of replicates to colonize all available surfaces.

These means of reproduction seem sufficient to maintain the species, but string algae has an additional strategy. It also forms akinetes, or cysts. These are microscopic versions of itself which are encapsulated in a hard outer cell wall and can be carried by the currents for long distances. These akinetes seem to form when growth conditions become unfavourable, such as in very cold water or when nutrient is unavailable. In one experiment, akinete formation was triggered by raising Cladophora in distilled water. These cysts can endure for long periods of time. How long does not seem to have been determined. It seems that decades are possible. Obviously, if they can endure for centuries, it will take centuries of study to find out.

Pull out just a single filament of string algae some time. Look at how thin it is, and how strong. Within it, there are three known means of reproduction potentially occurring, and that single filament is itself ready to grow if you just give it a spot of its own.

Currents

I had in mind to eventually do a post on the relationship of string algae with currents. Although I've not gone back to gather up materials on the subject, the question of currents has been raised. So, I'll post now and add more another time when I've had a chance to retrieve some studies. There have been a lot of studies, particularly in regard to marine species that thrive in the constant turbulence of coastal rock zones and tidepools. The freshwater studies are interesting, too.

The key trait of string algae is the strength of the filaments and their flexibility. Few life forms combine both to such a degree. We have all observed that string algae thrives in strong currents. If it is present, it will be abundant on waterfalls and where currents are strong along pond walls. The strength and flexibility of the filament allows it to resist abrasion where other alga could not. Also, the holdfasts put down by string algae are very strong, and intertwine with those of each plant. The thousands composing a single clump create a strong bond with the substrate like a form of cement. Even if unusually strong flooding currents cause breakage of filaments, the clump is likely to remain held in place.

The physical appearance of string algae is much influenced by currents. There are a couple of aspects to this. First, as flow velocities increase, the filaments lengthen. Also, the cell walls become more thin. And, third, branching of filaments can occur, resulting in extremely long streamers of filaments. These changes have further consequences. The individual filaments are more able to take in CO2 and nutrients, and both CO2 and nutrients are more available at the molecular surface due to the continual flow over the surface of the filament. Studies have shown that string algae that was utilizing bicarbonates as a carbon source in low current conditions was able to decrease reliance on bicarbonates and directly use more dissolved atmospheric CO2 as currents were increased. This was perhaps due to the greater availability of CO2, and it being a more efficient source of carbon than the more complex bicarbonates formed in water.

So, with more efficiency in absorbing available nutrient, and increased availability of efficiently used nutrient, string algae thrives in currents. It is not that highly oxygenated water is preferred, oxygen is a waste product of photosynthesis. Rather, it is increased availability of CO2 and other nutrients along the outer cell membrane that seems to generate higher growth rates.

However, high currents can become a negative over time. The currents cause compaction of the streamers of algae. As compaction occurs, the velocity of water movement within the streamer decreases, meaning a reduction in nutrient availability to the filaments in the center. Also, compaction results in lowered light levels within the streamer. Studies have shown a decrease in the overall rate of photosynthesis in the biomass of filaments as compaction occurs. As the center of a streaming clump declines, there can be dead or dying filaments within it. The branching of filaments that occurs in currents contributes to the mass becoming increasingly intertwined, holding some dead/dying filaments in the interwoven matrix of filaments. So, we see a life stage transition from long flowing streamers to ones that have clumps within the streamers as the algae ages.

Thus, currents are a mixed blessing, both stimulating growth and contributing to decline.

Light

We all know that plants need light to live. It is essential to photosynthesis. Some plants prefer shade. Some prefer full sun. Put a shade plant in full sun and it will be scorched and eventually die. Put a sun-loving plant in deep shade and it will wither over time. These are simple observations we have all learned in our personal experiences. We tend to categorize all plants in this manner. However, some are adaptable to a very broad range of light exposure. There has been a great deal of study of the relationship of light and photosynthesis in string algae. (I guess it is an easy lab subject, because otherwise I do not know why so much attention has been given to it.) Although there have been a lot of inconsistent results, one theme that rings true throughout is that Cladophora exhibits positive photosynthetic activity at low light levels even in cool water. One study found that even in water as cold as 5C [41F], there was net positive photosynthesis at light levels as low as 35 uE, and even lower light levels have been sufficient at slightly higher temperatures. [The light studies use a measure of photosynthesis-irradiance that is rather too complex to explain here. It focuses on how many millioniths of a mole of photons reach a square meter of surface in one second, which I refer to as a uE (micro-einstein). These measurements are helpful for comparative purposes and focus on light in the spectral range useable by plants. There is something like 2,000 uE hitting the surface of the earth at noon at the equator on a perfectly clear, cloudless day in a desert (i.e., no humidity), and probably more like 1,400 if you leave the desert, add a normal haze and humidity. So, 35 uE is rather weak light.] The main points I gain from these studies is that string algae is well-adapted not only for tree-lined streams, but also for weak winter sun. It will still be growing, albeit very slowly, when almost nothing else is.

There have been efforts to identify optimal light levels, but I have found these fairly useless from a practical pondkeeper perspective because the results are so inter-related with temperature, nutrient availability and all sorts of other factors. As one might expect, as temperature rises, the optimal light level increases (until temperature is quite warm, interfering with plant metabolism). So, as water warms in the Spring, and the sun intensity is increasing, the string algae can use the increased light intensity for highly efficient growth.

There are also many studies trying to identify saturation points, the intensities at which additional light does not produce additional growth; and studies on photo-inhibition, trying to learn the light levels at which photosynthesis is reduced due to the light being too intense. Again, the results vary significantly according to numerous factors. However, one aspect that seems to hold true is that photo-inhibition rarely occurs, even when light intensities are quite higher than the saturation point. This low level of photo-inhibition has led to consideration of how string algae protects itself from too much sun. It seems to be that it can simply endure a lot of very intense light. It's growth habit also assists. In Nature, currents result in light being very unevenly distributed within the water, with the result that exposure to overly intense light would have to be measured in fractions of seconds. Clumps of filaments are also self-shading as they continuously wave through the water, over one another. And, the epiphyte community colonizing the surfaces provide shading. When photo-inhibition has been observed, it has involved high stress conditions, such as extreme temperatures, increased salinity, low available nutrient.

One group of studies I have found interesting concern string algae blooms in the Great Lakes that were mystifying observers because they were occurring in areas where nutrient pollution was significantly lowered. Why would string algae experience a population explosion when nutrient was reduced? The answer appears to be the proliferation of the freshwater mussels that have invaded as exotics carried by ships. In areas where the mussels are well-established, water clarity has greatly improved. The mussels are filter feeders, and eliminate turbidity otherwise present. In some areas, water clarity has increased from visibility limits of a couple of feet, to depths of dozens of feet. As clarity increased, string algae residing on rocks on the lake bottom became robust, and deeper areas of lake bottom became suitable habitat. The bloom was not caused by nutrient pollution, nor decreasing pollution, but by increased water clarity. I find it ironic that as we pondkeepers work to create clear water, using UV to get rid of the unicellular greenwater algae, adding media to entrap fines, we are improving conditions for string algae to fully use what nutrient is available.

Once again, that bothersome question comes to mind: With all we do make nutrient available and conditions near-perfect for string algae, and as adaptable as it is, why doesn't it overwhelm our koi ponds all the time?

Temperature

Since light and temperature appear to work in tandem when it comes to the rate of photosynthesis in string algae, it seems logical to address temperature at this point. There are a number of studies that report findings concerning the optimal temperature range for Cladaphora glomerata growth. However, they differ. An often repeated finding is that 15C-25C (59F-77F) is optimal. Studies of string algae growth in particular lakes often have somewhat different findings. One Great Lakes study came in at significantly lower temperatures, 10C-22C; and another established a range of 13C -17C. The problem I have with all of the 'optimal range' conclusions is that they may well be accurate for the particular study, but without having every parameter affecting growth measured, one cannot be sure what to attribute to temperature. Even in controlled laboratory experiments, the spectral range of the lighting is a variable that may alter results from one lab to another. What does come through clearly is that 'optimal temperature' is directly related to light. One study demonstrated this very dramatically. String algae grown at 10C (50F) at a particular irradiance level had only a negligibly lower rate of photosynthesis compared to string algae grown at the same irradiance level at 15C (59F). When the light irradiance was cut in half, the string algae grown at 10C had a photosynthesis rate of less than half of the string algae grown at 15C. Similar relationships have been found at other light and temperature levels in other studies. So, at low light levels, like the weak sun of winter, string algae will grow more if the water is warmer. Shading will reduce growth compared to what it otherwise would have been, but as water warms the extra shading may do no more than maintain the rate of growth the algae had at lower water temperatures.

The studies I have seen reach differing conclusions on the upper temperature limits for string algae. There is consistency in finding that at some high temperature level, string algae populations collapse. The multiplicity of factors that make the 'collapse point' 29C (84F) in one study and over 35C (over 95F) in another, have not been figured out as far as I am aware. The inconsistencies include one study where maximal growth was reached at 30C (86F), a temperature point where populations had collapsed in other studies. Nonetheless, there are repeated findings that photosynthesis rates and efficient utilization of nutrient go into decline as the water temperature exceeds 25C (77F), and some studies where the decline began at temperatures as low as 23C (73.4F). My conclusion from this is that results will vary from pond to pond, but there will be a temperature point where decline sets in. Hopefully for the pondkeeper, that temperature point will be one consistent with the well-being of the fish.

An interesting observation made in studies of string algae in natural waterbodies in various parts of the world with temperate climates, that is, where there are true seasonal changes, is that string algae dies off in mid-summer. What I find interesting is that midsummer in northern Michigan is nothing like mid-summer in the Grand Canyon. (I also notice that the term 'midsummer' does not have a universal meaning. For some, midsummer is in late June. For others, it is in mid-August.) It makes me think there are factors involved which have not been identified.

I'll toss out a thought for folks to tuck in the back of their minds. Consider the destructive process of production of zoospores, which results in irreparable rupturing of cell walls. There are many plants in my garden which come into bloom according to the duration of the day, or the angle of sunlight. I have a clump of Vriesea (a type of bromeliad) growing in the garden where some plants bloom in May and some bloom in November, while other Vrieseas grown in the garden bloom during one period of the year only. The blooming habit of this one clump seems to makes no sense until one realizes that plants of sufficient maturity in the clump reliably bloom two months after the equinox, whether it is the Spring or Fall equinox. There may be an analogous trigger for zoospore production, with the population collapses observed in relation to increasing temperatures also being in relation to maturation and reproductive cycles, which are reached in that vague summer time period in Nature. Of course, temperature is directly involved in the growth and maturation process in all plant forms that I know about, so some correllation would certainly exist.

As a purely personal observation, I have not had string algae proliferate at water temperatures below 68F (20C). The usual seasonal growth usually begins in April with water temperatures in the range of 70-72F, and typically dies back by June when water temperatures are generally around 75-78F (24-26C). The bloom is generally a 6-week wonder, minor some years and substantial other years. In our ponds, of course, we do all sorts of things that create a very unnatural environment.

Impacts on Water

Since studies about use of string algae have been mentioned, that seems like a good starting point for today's post. And, yes, there are a lot of such studies going on.

Some years ago the focus was on string algae as a means for removing excessive nitrogen and phosphorous from polluted water, such as sewage plant effluent. It lost out to water hyacinths, but not because it was less effective. To the contrary, string algae was repeatedly found to be much more effective and more effective in a wider range of conditions. However, success in water purification requires removal of the pollutants through harvesting the plants used. String algae is just too difficult to harvest. Water hyacinths win the competition as a water purifier because of the comparative low cost of harvesting. Also, water hyacinth can be turned into a livestock feed ingredient more readily than the heavy masses of wet algae. For pondkeepers, of course, our goal of reducing nitrogen and phosphates in our pond water is as much about preventing excessive algal growth as anything else. But, string algae does reduce the ammonia, nitrite and nitrate that would otherwise affect our fish.

The more recent focus has been on the use of string algae to deal with industrial pollution. A lot of the studies come out of eastern Europe and China, where communist regimes did little to protect the environment, leaving some truly horrible contamination sites. These studies have established that string algae has an astounding ability to remove heavy metals from water, particularly lead, cadmium, chromium, copper and nickel. In optimal conditions, upon harvesting the algae has been found to contain as much as 400 times the concentration of lead as the water in which it was placed, nearly 500 times as much nickel, and almost as high a concentration of other dangerous metals. However, the rate of adsorption is highly dependent on pH and the chemical properties of the water. The most effective adsorption rates have been attained at pH levels far more acidic than koikeepers would ever want, with a pH of 4.0 being very effective. Water that acidic would challenge even such acid-loving aquarium fish as Discus. At a pH of just 6.0, significant decreases in adsorption occur. At the pH ranges we normally have in a koi pond, string algae will remove heavy metals (although much of the metals would precipitate and not be a bother anyway), but not at the amazing rates that make it a subject for studying as a contamination cure. The pH factor raises a point to consider. If in doing water changes there is an upward shift in pH, metals adsorbed by the string algae may be released. I emphasize 'may'. I am not aware of studies focused on the relatively small pH shifts koikeepers would experience. It would be more concern for those pondkeepers who do a once-per-year pond cleaning, which so often involves replacing water that has become acidic with water that is of a high pH. (But, of course, they have other more serious issues than heavy metals.) It should also be noted that calcium ions block the uptake of metals (by a type of competitive exclusion). Since calcium-based materials are often used for maintaining alkalinity, these will impact the extent to which metals are removed. So, altogether, it seems string algae has some beneficial impact on the water in our ponds through removal of heavy metals, but folks should not get overly excited by the idea.

Allelopathy

For those not familiar with allelopathy, it refers to how plants emit various chemicals harmful to other plants. It is the same sort of thing as occurs with molds and fungi releasing chemicals that kill bacteria, such as the chemical we turned into penicillin. Some desert plants release very strong chemicals that create dead zones around them, thereby monopolizing all water and nutrient in their square meter of the earth. In aquatic environments, far less dramatic examples of allelopathy are all around. Or, should I say, equally dramatic if you think about it? Healthy underwater vegetation would seem to be a great substrate for algae of all sorts. Why aren't all submerged aquatic plants totally covered with algae to the point of being killed by it? A major reason is that these plants release substances that make their surfaces repellant to most algae. Allelopathy studies concerning aquatic plants have focused on how plants combat algae and other plant species, not on the chemical weapons used by algae. However, one study I came across a couple of years ago is very interesting.

Scientists in Uruguay performed a series of experiments studying the effects of filamentous green algae (they used both Cladophora and Spirogyra species) on greenwater algae in small experimental ponds. Their lab work was supplemented by field observations of natural waterbodies, and they followed-up with use of algae filtrates as additives to greenwater. Their findings were that the filamentous green algae suppressed the growth of greenwater algae without regard to nutrient levels or nutrient additions or other conditions. Without regard to the initial concentration of greenwater algae, the presence of the filamentous green algae had a strong suppression effect. To confirm that allelopathy was involved, filamentous algae filtrates were added to greenwater. The result was suppressed growth in the greenwater algae exposed to the filtrates. The suppression observed in cohabitation was greater when water was warmed to optimal ranges for filamentous green algae growth. The particular allelochemicals responsible for the impact now need to be identified. It should be noted that alellochemicals studied in regard to various plants have been found to breakdown over rather short time periods (hours and days, not weeks or months) and are typically in a lethal concentration only at the leaf surface. The algal filtrates used in the experiments would have been highly concentrated.

Once one accepts the fact that plants release chemicals necessary to combat plant competitors, it is logical that filamentous algae would benefit from combating the light-blocking unicellular algae. However, the amount of chemical needed to be effective in a natural waterbody would seem to me to be far too great, unless it was quite persistent in the environment, which allelochemicals typically are not. In the closed confines of an aquarium or pond, I can more readily accept the notion of allelopathic impacts. I think there will be a good deal more knowledge gained in the field of allelopathy over the next decade. I expect what is already a complexity of interactions will prove to be even more complicated.

Diseases

There are a number of investigatory studies seeking to learn what diseases algae can suffer. The ones I have seen are mostly about marine species. When it comes to freshwater Cladophora species, there does not seem there is much of anything known. At least, I have not come across much. There is a fungus mold that has been shown to have substantial negative impact on string algae. This mold, Acremonium kiliense, inhibits growth and can cause chlorotic appearance. This is a common mold. Why it affects string algae when other funguses do not is something I've not seen in studies. As far as I am aware, it has not been established under what conditions the mold will infect string algae. Studies have shown that warm water coincides with the most significant negative effects, and it seems to have a greater impact during summer months than in other seasons. It is not clear to me whether the mold infections begin with healthy string algae, or are taking advantage of algae going into decline, as it often does in summer when water temperatures rise. 

Bacterial diseases do not appear to bother string algae. It does produce antibiotic chemicals, which are a subject for medical study. Of course, all sorts of bacteria come into play when the algae dies. I have personally observed that clumps of the stuff removed from my pond and tossed in the garden take a long time to breakdown into soil. Whether that is due to residual antibiotic effects of algal chemistry or the percentage of cellulose I do not know. That's a subject on my 'curious about it' list. 

There is also an unwritten 'get around to it some day' list. Finding studies concerning string algae diseases is on it.

Residents

A lot of creatures call string algae home. I previously mentioned the epiphytic diatoms with nitrogen-fixing capabilities. There are several species of diatoms that take up residence on the filaments. Joining them are various cyanobacteria species. These epiphytes can become quite thick, leading to some scientific speculation that as a clump of string algae matures, the epiphytes would block light from reaching chlorophyll within the filaments. When filaments are relatively free of epiphytes, the color is a bright green. As the epiphyte community reproduces, the color becomes darker. With a heavy presence of diatoms, there can be a brownish cast. With heavy growth of cyanobacteria, the color takes on a dark, bluish-green cast. Although a number of articles refer to the potential of epiphytes to cause a material loss in photosynthetic capacity, I have not come across studies specifically addressing the impact of the epiphytes. I've also not made a particular effort to locate such studies. That is on my unwritten 'get around to it some day' list. What has been consistently observed is that as the epiphytic community increases, the hydro-dynamics of string algae streamers change. There is more drag, and the streamers lose buoyancy. (Sediments captured in the filaments contribute to this as well.) The rate of current flow within a streamer declines, reducing the availability of nutrient to filaments in the center of the streamer. These effects have negative impacts on growth.

String algae also serves as a habitat for numerous insect species' larvae, with midge larva often being found in residence. There are a number of nematode species (round worms) and isopods (little crustaceans) that take up residence. In many instances these critters graze on the detritus captured in the filaments. Studies of the gut contents of these creatures show that many consume at least some of the string algae itself. Some insect larva have been found to have as much as 20% of the gut contents composed of string algae. Most of the time, however, the percentage is quite small, say around 2-5%. Whether the algae was consumed purposefully, or came along with detritus being consumed, I cannot say. Various freshwater shrimp seem to like living in the streamers. Some of these are filter feeders, which like to be where currents will bring their food to them. Some are grazers, which appear to clean the filaments of detritus and epiphytes. It is unclear to me to what extent freshwater shrimp will consume string algae. Some small percentage of gut contents being composed of string algae would be consistent with unintentional consumption. The Malaysian Prawn (a/k/a Giant Freshwater Prawn) can be commercially raised using string algae as a major food. Otherwise, the only reports I have come across referring to freshwater shrimp consuming string algae are in the plant aquarium hobby, where many report that the so-called Amano Shrimp will keep string algae from proliferating, but appear to be of little use in ridding an established bloom. Perhaps they only like the young growth tips, which may not contain much of the chemicals that make string algae unpalatable. I have not come across reports of significant damage being done to string algae by grazing shrimp. It has been observed that mayfly nymphs graze selectively on the apical tips of filaments, but not the mature portions of filaments.

Bacterial inhabitants vary considerably from place to place. Of major concern in several studies is the presence of bacteria harmful to human health, such as E. coli. String algae growing in the vicinity of sewage plants is often loaded with it, and it proliferates in rotting masses that come ashore at lakes. Since our koi ponds contain quite large amounts of macro digestive waste, I think we can (and should for safety purposes) assume that E. coli is in residence in substantial quantities. Whether or not the particular strains are comparatively virulent, none should be assumed to be innocuous.

And, of course, in nature string algae provides protection for fish fry, tadpoles and innumerable other creatures. It is also a trap for some creatures. Daphnia and various rotifers become entangled in it, and then become subjects of predation by creatures inhabiting the algae. Where daphnia are numerous, there are certain flatworms that take up residence, with the daphnia becoming their main food source… one they could never capture but for the entrapment by all those filaments.

So, as with so much that occurs in the bio-system of the koi pond, string algae is not just algae. There is a community of organisms, some consuming the string algae and many calling it home.

Food For Koi??

We have all seen our koi grazing on algae. Mine appear to nibble on it every day, mouthing the pond walls. However, I do not find much algae in the waste stools other than when the fish are being fasted. I figure they like the taste of all the creatures inhabiting the algae on the pond walls, but not so much the algae. Still, they do consume quite a bit when a fast is imposed on them. But, I've never seen them try to eat any string algae streamers. There are studies finding string algae among the gut contents of various carp species, as well as tilapia and other fish. Various percentages are calculated. Thus far, I have not seen a report on stomach contents where string algae content was much more than around 20%.

There is good reason for our omnivorous koi not eating string algae. First, string algae has a low ratio content of amino acids, relatively high cellulose content and comparatively high amounts of capric, lauric, myristic and palmitoleic fatty acids. These are fatty acids which are considered toxic when concentrated. Some have been used as insecticides. The result is that string algae is not a very good source of nutrition, it is hard to digest and it tastes bad.

However, all the insect larvae, diatoms, isopods, and other critters living in and on the string algae are very nutritious. It is not surprising that grazing occurs on algae growing on pond walls where the fish can suck in the resident critters. To get the ones growing on streaming filaments, the koi would have to consume the full filament. Obviously, they do not care to do so.

There are other algae species that are regularly consumed in quantity by fish; but, not string algae.

Controlling String Algae

I have hesitated to get into the subject of controlling string algae in a direct fashion. There are a variety of actions that can be taken, each of which has its adherents. As soon as one method is criticized, somebody will speak up about how it always works for them. One thing that can be said without drawing rational objection is that there is no cure for string algae that is consistent with longterm koikeeping. The most that can be done is to control it so that it does not detract as much from enjoyment of the pond. So, I will review some of the approaches and my thoughts about them for whatever it is worth.

A second thing I am comfortable saying about all the approaches in use is that they all work... for some people, in some ponds on some occasions. And, that nearly all do not work for some people in their ponds on some occasions. The methods that can work for everyone all the time in any pond are the ones which most risk the well-being of our koi.

I will group the methods and discuss each in separate posts:

1. Limiting Light & Nutrient
2. Chemical Treatments: Hydrogen Peroxide
3. Chemical Treatments: Copper
4. Chemical Treatments: PP
5. Chemical Treatments: Others
6. Barley Straw
7. Clay & Kitty Litter
8. High Tech Gizmos
9. Plecostomus
10. Bacterial Additives
11. Bog Gardens

Limiting Light & Nutrient

It should be obvious that string algae will not grow in complete darkness in distilled water. It should also be obvious that koi will not survive in distilled water and that there is not much about koikeeping that can be enjoyed in total darkesss. All we can do is try to find a balance point.

Shading the koi pond is a good start for keeping string algae within tolerable limits. It is not a complete solution for all ponds. String algae can thrive in shaded conditions, but will have less growth than if in high light conditions. Shading the pond does no harm to the koi. Indeed, many recommend shading from direct sun to obtain the best color and healthy skin. Sunburn has been known to occur on occasion.

Shading can be provided by having a cover over the pond. These can be structures with a solid roof where light comes in only from the sides, or a support structure for shadecloth (which comes in a variety of densities), or a latticework structure. How dense can the shade be made? Personal preferences come into play on this question. I think koi look fine under 80% shadecloth used for ferneries. For me, 90% shade becomes a bit much.

Another way to provide shading is to use one of the pond dyes that make the water a dark blue or black. These dyes can really work if dosed heavily, but the effect is temporary. Unless you do not care about the actual color of the koi you keep, dyeing the water a deep midnight blue is as unappealing as the string algae. The dyes marketed are supposedly 'fish safe', but that only means the fish do not die from the immediate exposure. Many dyes are known carcinogens and others are of concern. I do not think it is a good idea to use the dyes on a regular basis, even if the color does not bother you.

There are numerous posts on koi boards all around the world about how string algae was gotten under control after a shade structure was installed. And, there are numerous reports of how ponds were shaded and the string algae seemed as robust as ever. And, reports from those who initially reported that shading solved their problem, but the next season or some months later experience an overgrowth of string algae. As explained above, there are reasons disparate results will occur, since light, temperature and nutrient availability all work together. And, with all methods used, there is always the possibility that the supposed solution implemented had little to do with the algae dying back. It may simply have reached that point in its life cycle, or the pond temperature may have risen too high (or declined too low) for the algae to thrive.

Limiting nutrient in a koi pond seems the least likely method to get much noticeable results. There is always going to be excess nutrient. Still, we know ammonia is the much preferred nitrogen source compared to nitrate. So, being sure that bio-filters are appropriately sized and that turnover rates minimize the ambient ammonia level are good things to do. Remember, there is always ammonia in the pond water even if it is below the detectable limits of your test kit. Increasing currents to obtain higher turnover rates, however, may prove counter-productive. The nutrient level may decrease, say 50%, but faster currents are exposing the algal filaments to the remaining nutrient at a faster rate. The algae is not consuming nutrient from the water as a whole. It is grabbing what comes into contact with cell walls. You might think of it as counting the number of nutrient units coming into contact with the cell wall per second. The count will be higher in currents than in still water. Nonetheless, I would not recommend eliminating currents. Our ponds rely on current to move waste to the bottom drains, to exercise the fish and oxygenate the water. Our first concern is maximizing our koi. We should not compromise that goal. Having moderate stocking and avoiding excessive feeding is all for the good. Perhaps the koi will consume a bit more algae while grazing the pond walls. These are things we should do in any event.

There are plenty of well-maintained high-end koi ponds with low nitrate levels and no detectable ammonia that suffer string algae over growth to the point of clogging filters and drains. So, it is understandable that folks turn to chemical additives, my next topic.

Hydrogen Peroxide

Hydrogen peroxide will work, temporarily.

I do not know if Hydrogen Peroxide is the most frequently used chemical agent for treating string algae, but it does seem to be the most recommended on koi boards over the past 10 years. I avoid using chemicals in the pond and have no personal experience using HP. I have read a goodly number of postings about the experiences of others. There are a number of different recommended doses. The one I most frequently see is one pint of 3% HP per 1,000 gallons of pond water (roughly 3.5ppm concentration in the pond). Many report that this dosage did little good, while some report it was 'good enough'. One contributor to a watergardening site reports using 3% HP at a rate of one pint per 100 gallons [10 times the usual recommended dose... approx. 35ppm, which will kill fish over a couple of days]. Another reports sucess using 3% HP at a dosage of one pint per 1,000 gallons, repeating the treatment every 5 days until the algae was gone. Another reports that it kept coming back, so they treat with 3% HP at a rate of one pint per 1,000 gallons every week or two to keep it away. HP comes in different strengths, so any recommendation has to be considered in that light. The 3% HP is what is most commonly found on drugstore shelves in the U.S., but sometimes there will be 5% HP on the shelf. Read the label. For large ponds or to reduce costs, some recommend Baquacil, which is 27% HP. Sometimes sodium percarbonate is also recommended. It converts into HP when added to water.

There are many reports of fish being killed by use of HP. A few years ago Roddy Conrad discussed the kill ratios and variable experiences reported on koi and watergardening boards. The aquatic toxicity of HP is established: 50% of fish exposed to a concentration of HP of 100ppm would be dead within 24 hours. If the concentration was reduced to 22ppm, the fish would get along for 4 days before half were dead. At lesser concentrations, the kill ratio will decrease. These concentrations confuse some folks because they have read that HP can be used at a concentration of 100ppm to kill parasites. This is true, but it is deadly to the fish as well unless pond conditions are such that the HP is exhausted quickly. That's why we typically do not see HP being recommended for parasite treatment. Roddy explained that a heavy dose of HP might prove safe in a pond with a heavy growth of algae to consume the HP, but repeating the dose could be deadly to the fish. He had a friend who copied what Roddy did to rid a pond of a heavy infestation, but the friend's pond was not as full of algae. There was a massive fish kill. I am not aware of any koi specific studies concerning the safe concentration level for HP over time. It does seem that concentrations around 5ppm are generally considered 'safe'. In case of an overdose, the recommended neutralizer for HP is potassium permanganate. Add it a little at a time until the water just starts to become pinkish. Then add sodium thiosulphate to neutralize the PP.

When HP is used, as with other chemical killing agents, there will be masses of dead algae to deal with. One can expect filters to become clogged. The water will deteriorate from cell contents being released into the water. Plan on maintaining aeration and doing water changes.

I recommend against the use of any chemicals in a koi pond unless essential, such as using dechlor to neutralize chlorine introduced when performing water changes. While HP will kill string algae, it is indiscriminate. It will be killing beneficial organisms in the pond, and eating away at the fish. Just because they do not die does not mean that no harm was done.

The circumstances under which I might consider using HP would have to be rather extreme, such as algae blocking filters and drains at so rapid a pace that I could not deal with it through cleaning skimmers and such on a frequent basis. However, I know a lot of folks are not as rabidly opposed to use of chemicals as I am. If you are going to use HP, then I recommend following the one pint of 3% HP per 1,000 gallons dosage. If it does not sufficiently retard growth, wait a few days and then dose again. Keep in mind that there will not be an immediate elimination of the algae. There will be a reduction in growth. It may take a couple of days for the degree of damage done to the algae to be visible to you. And, do not get the idea that all of your algae problems will be solved. HP is a temporary treatment. If it happens you are treating just as the string algae is about to have a natural population collapse, it may seem it was the HP that cleared it away quickly.

Copper

This will be a short post.

I find it amazing that anyone would ever recommend use of copper in a koi pond for any purpose, but I come across such recommendations on various boards. Koi are especially sensitive to copper, more sensitive than many other types of fish. Copper can be added in a variety of formulations to kill algae, but never, never add it to a koi pond. Read the label of any concoction sold to get rid of algae. If copper appears on the label, do not use it.

And, BTW, there are gizmos on the market that cost big bucks that are designed to continually release small quantities of copper into the water. These gizmos are actually marketed for use with koi ponds, even if the real target market is composed of watergardeners. Just because a manufacturer says something is for use with koi ponds does not mean it is. UGH!!!

Potassium Permanganate

As with HP, PP will kill string algae, as well as everything else that lives in a pond. The most frequently recommended method for using PP to treat string algae is that espoused by Roddy Conrad some years back. He has been recommending HP over PP for string algae control for quite a number of years now, but since his approach to using PP is still repeated around on the boards, here it is:

"When I dose, I put in between 1.5 to 2.5 PPM of potassium permanganate, and add it slowly, depending on how I am adding it, which depends on the filtration system of my pond. I dropped the dosage to this level after repeatedly getting in trouble with fish stress at the recommended 4 PPM dosage. I am sure about the dosage, since I have confirmed my pond volume four different ways, and can weigh the potassium permanganate dose accurately when I choose to do so. Usually I add one heaping teaspoon per 1000 gallons for the practice of this dose. One heaping teaspoon of PP powder weighs 18 grams. 1000 gallons of water weighs 8,500 pounds. There are 454 grams to a pound, so 1000 gallons of water weighs 8,500 times 454 = 3.9 million grams. 2 PPM for 3.9 million grams would be 8 grams. One heaping teaspoon of the PP powder weighs 8 to 10 grams, depending on how high I heap the teaspoon, so the one heaping teaspoon dose per 1000 gallons is 2.0 to 2.5 PPM dose level.

On the day I dose, it is usually my schedule to do the following:

1. I bypass the biological filter, and I keep the mechanical filter in use. I design my system so this is accomplished in less than a minute. This means turn off pump flows to my trickle tower biological filters, and take the net bags of plastic scrub pads from the tank in my indoor pond outside to lay on the concrete patio in the air while the PP treatment is done on the pond. I usually start the treatment at about 9 AM. I start a good air pump through air stones into the pond to make sure oxygen stays high and mixing stays excellent.

2. I add the first dose; how I add it depends on filtration system of the pond. In my outside pond, I mix it in a bucket and slowly pour it all
around the pond, taking probably 10 minutes to accomplish the dose. In my indoor
pond, I have a 800 gallon settling tank into which I just add all the powder all at once since before any fish see the dose it becomes slowly and well mixed. I also keep a large air pump mixing the water in the indoor pond to avoid concentrated spots of PP in the water where the fish live. My indoor pond is a 4000-gallon system currently, set up in an unused room in the basement of our rather large house.

3. I come back in an hour or two to see if the water has any residual pink color. If the pink color is gone, I add the second 2 PPM dose the same way the first one was added.

4. I come back in two to three hours to see whether there is any residual pink, if there is, I wait longer, if there is not and residual pink color, I may add a third dose.

5. After doing this for a few years, I never add more than 3 doses in a given day, because the water gets too brown to tell if there is any residual pink color left.

6. After the pink is gone either the second or third time, I add one pint of 3% hydrogen peroxide per 1000 gallons of water to get rid of the brown manganese dioxide. The peroxide will both oxidize the brown ugly manganese dioxide (the spent form of the permanganate) to a colorless higher oxidation state of the manganese, and it will also react with the active pink permanganate to make non-toxic forms of manganese.

7. I leave the biological filter bypassed until the next morning, that way neither the potassium permanganate nor the hydrogen peroxide will kill the good bacteria. The peroxide can kill the biological filter as fast as the permanganate, but the lifetime of the peroxide is probably only a few hours in a pond environment.

8. I change whatever is required for the specific filter system to use biological filter again the next morning. "


That is the Conrad method. I DO NOT recommend it. I DO NOT recommend use of PP. It is dangerous stuff. Based on all I have read, HP is preferable as a chemical treatment for string algae. Even Roddy Conrad, who has been an active proponent of PP for all sorts of purposes, does not recommend PP for treating string algae. He recommends HP.

As with HP, PP is a temporary method. There are many reports of the algae returning (as well as reports of it not returning... at least not right away). The downside risks and negative impact on the pond bio-community are similar to those of HP, but more so. While Conrad's method avoids treating the bio-media in the filters, there is more to the beneficial bio-community than what is in the media. If properly done, a single treatment with PP should not cause permanent harm to koi. But, just as HP ends up getting used repeatedly by some, PP ends up being used repeatedly. This is not good. It will end up causing permanent damage to the gills, and can do more harm than that.

Other Chemicals: Salt

At one time, it was widely recommended that salt be used to get rid of string algae. The recommended dosage varied. But, it did not do much unless the salt dosage was at a level that killed plants in the watergarden. Indeed, even a dosage concentration of 0.6% seemed to cause a temporary setback, but sometimes the algae was reported to adjust to the salt and continue growing. I do not see salt being recommended much anymore.

What salt can be effectively used for is to keep the string algae from growing on the pond bottom around the bottom drains, where the growing algae can clog the drains. Get salt that is in big pieces or chunks and toss the chunks on top of the algae growing around and into the bottom drains. The algae it lands on will be killed. Large streamers may well go through the drain shortly afterwards, so be prepared to deal with it going to the first stage of the filtration system fed by the drains. I've read a report of it gunking up a sieve because it came through in too large a glob for the seive to handle.

Other Chemicals: F/MG

Formalin-based parasite treatments will setback string algae. Since these nearly always include malachite green, a potential carcinogen, I would not recommend using it.

I would note that I have noticed a few folks on other boards who post that they never get string algae also post about doing prophylactic treatments with F/MG medications in the Spring as the water warms, in the Summer and in the Fall, and sometimes more frequently 'just in case'. I do not think it is ever a good idea to use F/MG as a preventative. Those who do may avoid string algae problems as a 'side benefit', but this is not anything I'd ever suggest.

Other Chemicals: Algaecides

There are numerous algaecides on the market. Some contain copper. One has as its active ingredient sodium percarbonate, so it is actually a form of HP treatment. A variety of herbicides are also used. Thus far, I have not come across a single algaecide purporting to be 'fish safe' that did not result in fish deaths in a lot of folks' ponds. The manufacturers and retailers will say that it must not have been dosed properly. The pondkeeper will say that they followed the instructions precisely. All I can say is that there are a lot of folks in whose experience HP and PP have proved safer than any algaecide 'guaranteed fish safe when used as directed'. Since HP is cheaper than the algaecides, there is no reason to spend more and take greater risk.

Barley Straw

In the pond hobby's neverending search for a solution to string algae problems, the promotion of barley straw stands out to me. It is a mystical solution wrapped in scientific terms that seems to be science-based, but nobody understands what it does or how it works. In so many ways, it is an offspring of marketing with desperate hobbyists literally grasping for straws.

Barley straw is touted for algae control in all sorts of publications, and there are a lot of barley straw products on the market. I can only imagine the huge sums spent on these products annually. However, I seldom see pondkeepers extolling it as a remedy for algae, although there are frequent posts about folks using a barley straw extract in reaction to an outbreak of string algae. They will say such things as, 'I used barley straw extract, but this algae is just taking over everything. What can I do?' What amazes me, although I guess it shouldn't, is that there is actually quite a bit of scientific research into barley straw. The conclusions just do not seem to get fully reported.

Most studies done on barley straw have focused on its possible use for controlling algae in natural waterbodies. The notion of using barley straw grows out of its use in the UK in the 1990s in reservoirs for algae control purposes. The studies indicate that barley straw can be used to clear some species of algae, but not others. To date, I have not seen a single study find that barley straw has any impact on an existing population of string algae. Instead, the studies indicate it may affect unicellular greenwater algae and blue-green algae (cyanobacteria) adversely, but no impact on filamentous algae has been documented. (Impacts on blue-green algae have varied, raising the question of whether population declines actually were caused by use of barley straw or other coincidental factors. But, adverse effects have been documented on so many occasions that it seems likely there is an impact.) I repeat, as far as I am aware, there is not a single scientifically performed study indicating that barley straw is useful in eliminating an existing string algae population. There are studies indicating that it can adversely impact greenwater algae when used appropriately. So, a marketing claim that it is scientifically proven to fight algae may be literally true, but not string algae.

The studies most supportive of barley straw for use in controlling string algae may be ones conducted at the University of Florida. These indicate that barley straw does not have an algicidal effect. I repeat, NO algicidal effect. However, the studies suggest that barley straw may be algistatic, meaning that it may prevent or retard algae growth, but does nothing to eliminate established string algae. In the UK, researchers have suggested that barley straw requires months of use before significant impacts are observable, which would indicate that shorter duration experiments conducted in the U.S. were terminated too soon. British scientists studying barley straw have indicated that algistatic chemicals produced by decomposing barley straw build up in the water over a period of about 6 months and the effects will start becoming observable. However, since the particular chemicals have not been identified, we cannot know whether there are chemicals produced that are so persistent that it takes months for them to breakdown. The Brits who supported use of barley straw recommended that more barley straw be regularly added to have continuous decomposition.These recommendations are based on barley straw decomposing in the comparatively cool waters of the UK at a relatively slow rate. In warmer waters, decomposition proceeds more quickly, so replacement would have to occur more frequently. Studies also indicate that in turbid waters (muddy water) the amount of straw used must be increased. Whether this is due to algistatic chemicals being adsorbed by the mud in the water or sunlight being blocked does not seem to have been determined.

I have seen no scientific study of the utility of the so-called barley straw extracts sold in the ponding marketplace. Every study I have seen has concerned actual straw being allowed to decompose.

As far as I am aware, nobody really knows how barley straw works to retard algal growth, even the scientists who study it. The theories put forward include: (1) it releases oxidized polyphenolics during decomposition which inhibit algal growth; (2) the decomposition process, when occurring in sunlight, produces hydrogen peroxide in a weak concentration; and (3) barley straw is decomposed by a particular fungus and it is the fungus that produces a growth retarding chemical as a byproduct of its metabolism. (The idea of a build-up of algistatic chemical per the British advocates is contrary to the theory that hydrogen peroxide forms in the decomposition process and causes the retardation of growth. HP is not going to build-up in the water, and certainly not for 6 months.)

Whether or not barley straw can provide any practical benefit in some situations, and there is just enough science behind it to think there might be circumstances where it could have some impact, altogether I think it is a complete waste of money for the koikeeper. The reason is simple: Koi ponds should receive regular substantial water changes. That means that whatever barley straw might add to the water is going to be continually removed. Even the more ardent supporters of barley straw use in the scientific community speak in terms of patiently waiting for many months to observe positive results. And, by "many months" we are talking about 4-8 months continuous presence of decomposing barley straw. The idea of not performing water changes for many months is contrary to sound koikeeping practice. And, thinking a little bottle of extract can immediately accomplish what the scientific advocates say will take many months is... well, believing in snake oil IMO.

High Tech Gizmos

I guess calling algae control devices 'gizmos' declares my doubts about them as a class. I have no idea how many such devices are on the market. They seem to come and go. I already mentioned one that continually releases copper into the water, not a good thing for koi. There are others based on UV light, which does nothing to affect string algae. There are also dispensing gizmos that basically serve to continually dose the pond with one sort of algicide or another. I consider these sorts of devices as costly gimmicks that risk the well-being of the koi or do nothing to control string algae.

Then there is a group of devices that are actually reported by some to have a beneficial impact, although not touted by many users as completely eliminating string algae in toto. These are gizmos based on electro-magnetic radiation being generated to pulse through the pond water, usually at the point of a return line after the water has gone through the filtration system. It is a scientific fact that such a device, appropriately designed and installed, would reduce calcium bicarbonate ions and increase calcium carbonate ions. The length of time for which the altered ratio endures would vary according to water chemistry. Since calcium carbonate will then tend to precipitate as the concentration of it increases, there would end up being a reduction of total available calcium, unless water chemistry is such that it re-dissolved. There are several theories as to how this alteration of ion balance in the water might affect string algae. One is that the reduced availability of calcium in itself retards growth. Another theory is the exact opposite, that algal cell walls are better able to take in calcium when the ratio of bicarbonate and carbonate is altered, resulting in an increase in metabolism that leads to the string algae withering away as it tries to grow faster than available nutrient allows. …Huh??? Well, that's one of the theories about why these electro-magnetic radiation devices work, or appear to do so sometimes. A third theory is that the algal holdfasts weaken, causing algae to slough off the pond surfaces. But, do these devices actually work? I have to say that I'm always bothered when something is said to work, but the how cannot be consistently explained, particularly when someone is wanting large sums of money. Well, there have been non-scientific 'consumer trials' where use of the devices has been said to reduce string algae by the pond owner. So, some folks really believe they can work. I note that one manufacturer claims that great results will be obtained after 12 weeks of continuous use. Another says growth ceases as soon as 10 days after commencing use and the full impact will be seen in 7-10 weeks. It is also said by some that the devices should be turned off when the water is cool because the ion re-balancing will cause growth of the dreaded string algae in cool water. OK, I think I understand. Use the devices only when the water is warming up, and after 3 months the full benefits will be observed. … Why do I keep thinking that coincides with the natural life cycle of string algae?? These are costly devices, prone to breaking (if postings on koi boards are to be believed). When a consumer says they do not work, a manufacturer will say the device was not properly installed or not enough time was allowed. Another consumer will come along saying that after months of battling string algae they installed the device and had complete relief in the course of several days… Huh?? The manufacturer says it will take a couple of months, but the consumer got relief in days? I am left thinking that coincidence has sold a lot of these gizmos. I really have no idea whether they accomplish anything, or perhaps are effective in certain particular conditions. As long as consumer experience is mixed, I tend to suspect the device accomplishes nothing. 

If anyone has a gizmo that they believe actually worked for them, please post about it.

Musing about Climate Conditions

Yes, it is a mystery, Ric.

My pond experiences a seasonal bloom each year. Some years it is minor. Some years it is substantial. I do not know why it varies. I have noticed that the years when the outbreak has been most serious are also ones when I did not have any parasite outbreaks. That means there was no treatment for parasites. For most parasites, I use Pro-form C (F/MG) , which will setback algae. So, that may have been a factor in those years; but, perhaps not a complete explanation. One of the worse years for string algae in my pond was 5 or so years ago. In the course of a couple of weeks the pond went from some string algae being observed to a super-abundant explosion of the stuff. I was having to clean filter mats in the skimmers daily. The leaf baskets on pumps had to checked daily. Huge globs came through the bottom drains when flushed. The total algae production was incredible. When I called a friend I learned that he also was having an unprecedented string algae problem, as was another local hobbyist with multiple ponds. All of these ponds were designed as true koi ponds with all the filtration systems one could want and regularly maintained with daily attention. All of these ponds had different water sources... two different public utilities and private wells. The source water could not have been the causative factor. The unusually robust string algae growth was occurring throughout the Orlando region. It cannot be scientifically established, but I do believe that outbreak across the region had more to do with climatic conditions that year than pond-specific issues. Perhaps it was the number of days with water temperatures in a particular range. Perhaps conditions the prior Fall laid the ground for abundant growth when certain conditions came together that particular Spring. I simply do not know. Still, I have a hard time thinking it was coincidental that so many ponds in the area experienced an abundance of string algae much greater than any of the hobbyists had experienced previously. And, all of the ponds had the algae decline around the same time. It was about 6 weeks of misery. By late June, when even shaded ponds in the area have temperatures in the upper 70sF, you could visit the different ponds and not have a clue there had been such problems so short a time before.

Plecostomus

The algae-eating Plecostomus catfish is sometimes mentioned as a means to combat algae in the koi pond. I can speak with some experience about them. They will consume tremendous amounts of algae. They are not going to consume streamers in the water column. They will consume all algae on the pond walls and floor. If you do not feed sinking food, with a few plecostomus in the pond, and the water warm, in time there will be no significant amount of algae on any surface readily accessible… no string algae, no carpet algae, no algae at all. Their diet can be supplemented with sinking food. Although they are algae-eaters, they will go after meaty foods if available. Their algae consumption will be much reduced if other foods are made available. Of course, when the pond temperature falls below 70F they do not eat much and die if the water temperature stays in the low 60sF (or lower) for very long. So, they are not going to be of much use to anyone who is not in a warm water/subtropical area. There is a potential problem. If they do not have plenty of algae or other food to eat, they have been known to go after the slimecoat of other fish. This means our koi are placed at risk of injury. In a small pond with just goldfish and truly small koi, one or two plecos seem to do fine and do not bother the koi if enough food is provided so they do not have to rely solely on algae. The small fish are fast. As koi get larger, however, they are bigger targets and not as quick. Plecos are nocturnally active, so you might not see the attacks on your koi occurring. The Plecos can become a real problem. For those with goldfish in a watergarden, the plecos may work well, but they do like their veggies in all forms. When I kept a pleco in my lily pond the waterlillies were left alone. No other plant was left unconsumed.

For the koi pond, I do not recommend keeping plecos even in warm climates. They may provide a real assist in controlling algae, but also present a risk to the koi that are the focus of our attention. You might get away with it for a while, but eventually you are likely to wish you had not put them in the pond.

Clay & Kitty Litter

I often see folks recommending the use of powdered clay to control string algae. Some swear by it. Others say it does them no good. Some say they have no idea whether it does any good, but it makes them feel good to try something. Since the bentonite clays adsorb ammonia and some phosphates, among other things, there is some logic to the notion of using clay. It can reduce the availability of nutrient for a short period. As soon as it settles out of the water column, however, the effect is reduced. As much impact may come from it being captured in the filaments of string algae, where it blocks light to some degree. Studies have shown that string algae does not fare well in natural waterbodies where silt released from dams and the like clog the streamers.

Personally, I have used clay in the past and cannot say there was any impact on the string algae. However, I did not apply it daily over an extended period. Logically, it would have to be used repeatedly in order for the nutrient scrubbing to have much of an effect. Unlike chemical additives, clay on the market for use with koi will not harm the koi. So, if a person has clay on hand, they might as well use it.

A related method recommended by some is to place a tub of kitty litter in the pond. Now, I know regulars on this board are ready to roll over howling at the suggestion, but since some folks say it works, it has to be recognized as a method in use. (BTW, the kitty litter generally suggested is the cheapest sold at Walmart, which has no perfumes or additives, but is 100% bentonite, albeit not necessarily of the grade considered suitable for consumption.) Those who recommend this practice theorize that the tub of litter allows water to flow through, and continually adsorbs nutrient that would otherwise feed the algae. One proponent plants their waterlillies in tubs of kitty litter and claims to never have string algae issues. I have seen a number of posts by people saying they were going to try this method. I have not seen much in follow-up posts reporting it was successful for them. I can imagine that bentonite clay might be an acceptable planting medium for waterlillies, although I have not seen it recommended by any expert growers. I do not think there would be much water movement through the clay. The reason it is used as cat litter is because it absorbs and holds liquid, and does not let the liquid flow through. It is used to line mudponds in areas with a low water table because it will hold the water in the pond. Water flows through bentonite clay very slowly even when gravity is working in favor of it moving through. So, I do not see the tub of clay as doing much of anything. However, thriving waterlillies would block sunlight. So, the method might seem to work. In any event, for the koikeeper, this is not a practical approach. A tub in the pond is simply something else on which koi might injure themselves. If I am going to use clay, I would not use kitty litter. I would use powdered clay applied in daily doses to the water column.

        Bacterial Additives

Now I come to what may be as much 'scientific' snake oil as barley straw extract, or may be a useful tool in the control of string algae. I suspect some bacterial concoction may be truly helpful and I find the subject intrigueing, but I decline to vouch for any product and do not want to encourage anyone to spend money on 'bottled bugs'. Still....

We do not see much about using bacterial additives to combat string algae in the U.S. It is a topic of discussion elsewhere, particularly in the UK. I first got interested in the possibility after I used a sludge remover concoction because I was concerned about debris build-up in a plumbing run that I cannot easily flush. There was a die-back of algae in the weeks thereafter. Whether it was coincidence or causative, I had no idea. And, some years ago, after the regional outbreak I mentioned above, a friend obtained a Viresco bacterial additive from the UK and it seemed to him to have a negative effect on string algae. So, I tried reading up on the subject, only to find that the mass of science involved is more confusing and complex than trying to understand string algae. There is no end to the trails one can wander. Nonetheless, what I learned in perusing articles on sewage waste treatment and such was enough to make me think that a useful concoction is possible. Whether one actually exists, and whether the ones marketed actually work (even if not quite as well as the promoters say), I have not decided.

Based on what I have seen on UK-based koi forums, the Viresco line of additives seems to be the most successful in the marketplace. The story line is that in the course of producing sludge-consuming concoctions, it was observed that there were negative impacts on string algae. (That tale appeals to me since I think I observed the same thing, or deluded myself into thinking I had.) So, the little family business played around and refined the concoction to emphasize certain anaerobic bacteria which consume nitrate and phosphate. The identity of these magic bacteria is kept as guarded trade secret. (What silliness! If this little family business figured it out, so could the large companies heavily invested in the sewage treatment industry with staffs of scientists studying microbes all the time. I figure that they either don't know, or the bacteria are available much more cheaply from an industrial supply source.) The anaerobic bacteria in the Viresco product supposedly take up residence in the anaerobic micro-environments of the pond, particularly in the bio-film. There they proliferate, consuming nitrate to the point that it becomes undetectable and lowering phosphate levels substantially (but not completely). String algae populations will begin to collapse in about 10 days, they say, and the string algae will be fully under control after about 30 days. But, if good results are not seen, a second treatment may be needed. Hmmmm... if the bacteria are proliferating like crazy as it is said they do, why would a second treatment be needed? It should not take much time for a bacterial population to multiply to a point equivalent to what is in a little package of the product. Sounds more like fantasy than fantastic.

But, Viresco has a lot of supporters on UK boards, as well as those who say it did not work for them. I used it one year and experienced a decline in string algae, but I used it just before temperatures soared, so it could have been pure coincidence. The company proudly claims that a huge percentage of sales are to repeat customers. And, a series of popular magazine articles purporting to study the effectiveness of the product gave it high marks for controlling string algae. (Although in one it was used in two tubs to which a glob of algae was added, with apparent success in one tub and not in the other, until a repeat dose was applied, at which point the two week study ended. Hmmm.) It all has the sound of barley straw extract, but my friend thought it helped and I saw the coincidental effect of using sludge remover, right? So, I decided to look into it some more.

I'll not trace the confusing mess of 'stuff' written in the microbiology sub-field of waste treatment. It is a busy field for researchers. I did come across articles about using alternating anaerobic and aerobic processes to reduce or eliminate nitrate and phosphate from sewage wastewater. And, I found an article about a particular anaerobic critter that could do the trick without the alternating stages. ...The article abstract is informative, even if a challenge on first reading:

Applied And Environmental Microbiology, March, 2000 : "Polyphosphate accumulation by Paracoccus denitrificans was examined under aerobic, anoxic, and anaerobic conditions. Polyphosphate synthesis by this denitrifier took place with either oxygen or nitrate as the electron acceptor and in the presence of an external carbon source. Cells were capable of poly-β-hydroxybutyrate (PHB) synthesis, but no polyphosphate was produced when PHB-rich cells were incubated under anoxic conditions in the absence of an external carbon source. By comparison of these findings to those with polyphosphate-accumulating organisms thought to be responsible for phosphate removal in activated sludge systems, it is concluded that P. denitrificans is capable of combined phosphate and nitrate removal without the need for alternating anaerobic/aerobic or anaerobic/anoxic switches. Studies on additional denitrifying isolates from a denitrifying fluidized bed reactor suggested that polyphosphate accumulation is widespread among denitrifiers."

So, it is possible to lower both nitrate and phosphate levels using anaerobic bacteria. Can it be done by just adding the critters to the highly oxygenated koi pond? If there are suitable habitats for these wondrous bacteria, how is it that they cannot find their way into my pond without being purchased? And, since there is a continual supply of nitrate and phosphate in the koi pond, why would there ever be a need for more than one application throughout the life of the pond? I guess I just can't stop asking questions.

The promoter of the product says it is the removal of nitrate that causes string algae to decline. However, it is established that string algae do not use much nitrate. If they did, nitrate levels would plummet when string algae bloomed. But, use of nitrate does occur if phosphate levels are high. If the Viresco bugs do work, I suspect it is due to the lowering of phosphate as much as, or more than, lowering of nitrate.

Altogether, I remain intrigued by the possibility. I wonder why the U.S. bottled bugs producers do not aim a product at string algae. And, I wonder if it is waste of money to go on Ebay and click on 'Buy It Now'. It would cost about $85 to treat my pond. Or, just wait for the string algae to decline on its own, as it always seems to do by late June. Since it's early June, I guess I'll worry about it next year. Meanwhile, I'll be wondering if it just might work, in the right conditions. ...but, why did the second tub need a repeat application when the two tubs were set up identically?

Bog Gardens: Revisiting Norm Meck's Theories

If anyone was paying closer attention than any sane person should, they would have noted that I did not include bog gardens on the initial list of remedies. I added it along the way. I had not included bog gardens initially, I guess because I am so biased against the notion of them. I have blasted the idea that a bog garden will purify pond water through nitrogen removal in another thread. However, I was planning to revisit theories put forward by Norm Meck a dozen or more years ago, and as I thought about it, it seemed to me that the bog garden topic served that goal.

There are folks who repeatedly post that they never have a string algae problem and credit it to the wonderful bog garden they rely upon to purify their pond. They credit the bog with removing nitrogen from the system so that string algae cannot take hold. This is simply silly. As I have explained at length in that other thread, the amount of vegetation required to have an effect on a koi pond is hugely more than any bog garden, and the nitrogen removal would have to be so substantial that the garden would not be the thriving, beautiful creation people are so proud to have. However, that does not mean the bog garden may not have an impact on algae. The impact is not due to nitrogen removal. If there is one, it is due to decomposition occurring in the bog. And, that takes us to Ray Jordan's post about pondkeepers who do everything wrong and do not get string algae, and Norm Meck's theory.

Newcomers may not know about Norm Meck. He had a background in wastewater treatment and sewage plants. He frequently contributed to popular koi literature in the 1980s and 1990s in regard to filtration, water chemistry and nitrification processes. He had a special interest in greenwater and undertook a determined study of the phenomenon. Best known are the series of experiments he conducted in which water from many different sources were used to culture greenwater. He used distilled water, tap water, well water and water from different established ponds that were clear. (These were ponds that did not rely on UV to be clear.) Adding nutrient, aeration and a 'starter culture' of greenwater, he found that that the greenwater alga rapidly grew in all the samples except the ones from established clear ponds. Starter algae added to those samples died within a few hours. From these experiments, he concluded that there was some substance in clear established pond water that is toxic to greenwater algae. In the years following his initial experiments, he proceeded to try to identify what that substance was. He did not succeed, but did put forward a theory. That theory is that aerobic decomposition of algae by heterotroph bacteria releases a by-product toxic to living algae. He considered this substance an antibiotic, using that term in its broad sense. (At one time, he theorized that the toxic substance was released by the dead algae itself, but his studies led to him rejecting that idea in favor of the decomposition by-product theory.) He suspected the source was the lignin in the cellulose making up algal cell walls, and noted that barley straw has a similar cellular composition, which might explain the anti-algal effects of decomposing barley straw showing up in early studies occurring when he was getting deeply into the subject. Meck performed an additional set of experiments which led him to believe it likely that the substance persisted for only a few days, perhaps no more than 4 days, but he did not confirm this. He also performed experiments in which clear pond water was diluted with distilled water. These showed that at a 50-50 dilution, greenwater algae died quickly. In two parts distilled water and one part clear pond water, the algae did not die, but did not grow. At a 3:1 dilution, growth occurred at slower rates. At a 4:1 dilution, the algae flourished. These experiments confirmed the conclusion that the toxic substance exists. Meck also came to think that UV radiation might destroy the substance, whatever it was.

The Meck studies indicate why a bog garden may actually work in fighting string algae, since we know they are usually a center of decomposition. If Meck was correct that the toxic substance comes from the decomposition of cellulose, then decomposition of any vegetative matter would do. Some plants have a higher ratio of cellulose than others, but all have quite a large proportion of the cell wall composed of cellulose. However, the effectiveness would depend on there being only small or no water changes. The toxic substance would have to be allowed to build up in the water. In other words, an ill-maintained pond with decomposing plant-based organics (leaves and such), just might have so much of the toxic substance that string algae is deterred. Cleaning gunk out of filters regularly, rapid removal of organic wastes through bottom drains, frequent large water changes... all the things we have learned to do in maintaining our ponds, these minimize the presence of Meck's toxic substance.

I do not recommend that koikeepers give up their maintenance chores. Doing so might help combat the inconvenience of string algae, but our koi do come first.

Meck Theory Postscript

Meck came to believe that heterotrohic bacterial decomposition and not nitrifier competition was the reason well-filtered ponds could stay clear. I disagree with this aspect of his work. I think it is now too well established that nitrifier competition can deter greenwater algae. Using my own pond as a negating example, I perform huge water changes weekly that would so dilute the toxic substance that greenwater algae should be thriving in my pond. Even without the use of UV, greenwater does not thrive. The water is clear to the eye of visitors.

While I reject this aspect of Meck's thinking, I do believe there is merit to the main conclusion that there is an algicidal substance released in the course of decomposition. It is another variable among the many mentioned thus far in this thread, all contributing to the apparent inconsistencies and mystery of string algae.


________________


Another Chemical: Sodium Bromide & Chlorine

I learned this week of another chemical being used to control algae. On another board a fellow reports that he went to a pond shop asking for help in dealing with a serious outbreak of string algae. The shop owner went into the back of his shop and 'mixed up some Black Magic' and brought out a blackish liquid. The fellow put in it his pond and in short order there was a massive die-off of the algae. It is not certain what the fellow was given, but 'Black Magic' is the brand name of a product used in the swimming pool industry to rid pools of algae when mixed with chlorine. (Perhaps some chlorine was added when it was mixed up in the back of the shop??) It is simply sodium bromide, which is used with chlorine to create a bromine acid in a swimming pool. Most folks are familiar with using chlorine in swimming pools for continuous disinfectant. Another approach is what is called a 'bromine pool'. [Those with a hot tub may be using sodium bromide. It is often preferred because chlorine gasses off very quickly in heated water with turbulent aeration. I am told that bromine pools are not often seen because it is more expensive than using chlorine and some folks get rashes caused by bromine.] With bromine, there is long persistence, unlike chlorine which gasses off. Reading up on the subject a bit (but not enough to be 100% sure of things), it seems bromine that gets broken down by sunlight or that oxidizes an organic becomes bromide which then gets reactivated by chlorine in the water to become bromine again, such as by topping up the pool with chlorinated tap water. Bromine or bromide only leave the system through very slow off-gassing (measured in several months, not weeks or days) or water changes. In other words:

Bromide + Chlorine ---> Bromine + Chloride
Bromine broken down by sunlight or oxidizing ammonia or an organic ---> Bromide

Only water changes gets rid of it. It is not used in swimming pools as much as chlorine because it is much more complex to monitor and keep in safe and effective sanitizing ranges.

In a pond, the bromine acid will kill algae and all other living things, converting back to bromide. If the algae comes back in a month or so, a second treatment cannot be given until the residual bromide is determined, which is very difficult to do. It seems it shows up on salinity tests, but one cannot know if the salinity is caused by sodium bromide or sodium chloride or another salt. Like PP, there is a balancing act in having a strong enough concentration to kill what the pondkeeper wants dead and not killing the koi. If a second dosing occurs, the bromine level could be twice the concentration intended. Since I am not aware of studies concerning its use with fish, I am not about to make any suggestions as to what the 'balance' might be. And, what 'works' in a pond loaded with string algae may well be deadly in other circumstances. Unlike the oxidizers used in the hobby, bromide will stay in the pond, converting back to poisonous bromine whenever something is added that triggers the reaction. It does not have to be chlorine.

I am posting about this for two reasons. First, if anybody is tempted to use sodium bromide, DON'T! ... As much as I dislike the use of potassium permanganate, it would be a much safer choice, just as effective and without the persistent presence creating all sorts of risks. Second, just because somebody says something worked for them, don't mindlessly follow the suggestion... even the suggestion of the guy who owns a pond supply shop. People do dumb things. Copying them is not a smart thing. Do not put something in your pond without knowing what it is, how it works and what the consequences may be.

Better living is not always about chemistry.

Controlling String Algae: The Algal Turf Scrubber

With the water warming, complaints about string algae are becoming a subject of discussion on some boards. A new twist has popped up, with the suggestion that one's string algae problems can be solved by installing an algal turf scrubber. Never heard of an algal turf scrubber? Well, I have never heard of them being used on ponds, but it was all the rage in the reef aquarium hobby years ago. You can think of the ATS as an algae version of a bog garden. The idea is to have a highly efficient algae habitat that will be so productive that nutrients will be used up to the point that algae will not grow well in the pond, because it is flourishing so wildly in the ATS. I am not aware of anyone having successfully adapted the ATS concept to a koi pond. I do not believe it can be done. In theory it might be done to reduce the need for water changes, the motivating factor behind efforts to use ATS on reef aquaria, but the notion that it can be implemented so effectively that algae will thrive in the ATS, but waste away in the pond, seems quite illogical to me.

That is not to say that the ATS concept cannot have useful applications for the engineering-minded. It just is not practical IMO.

The ATS was first promoted by Dr. Walter Adey, following much research into reef-keeeping. He is known for having a huge coral reef aquarium maintained for many years through use of an ATS system. In his book, Dynamic Aquaria, Dr Adey set forth the scientific principles behind the ATS. Basically, the ATS received light 24-hours a day, allowing the algae cultivated in it to not only consume nutrient, but to offset CO2 produced at night in the aquarium thereby preventing acidification. It was quite successful in his skilled, careful hands. ...Until it wasn't. It eventually was learned that the ATS removed not only negative nutrients, but also beneficial ones. So, to maintain coral growth, there had to be regular controlled additions of calcium, strontium and other minerals. Nonetheless, the success experienced led to a fad of all sorts of DIY ATS designs. These either did not work as promised, or proved to be quite expensive. A whole lot more technology and skilled attentiveness was required than even reef aquarists were willing to devote. (Of course, there were those exceptional individuals who knew no limits on the time and expense devoted to their mini oceans.) A variation then came along, called 'the refugium', in which algae was grown in a sump attached to the reef aquarium to help reduce the need for water changes to control nutrients that promoted algae growth in the aquarium. However, refugiums did not consume nutrient fast enough to prevent algae in the aquarium. And, the need to harvest algae to actually remove nutrient from the system was as much of a hassle as performing a water change. And, if the algae was not harvested regularly, its growth would block light reaching the lower levels, leading to an algae die-off that returned undesired nutrient to the aquarium. You will find refugiums still in use, but today they are not seen as a cure-all they were once promoted to be. Rather, by providing a habitat where little organisms could grow and reproduce, they are as much a source of live food supplementing the diet of the reef inhabitants as anything else.

I think of ATS as an algae version of the bog garden that is supposed to purify the pond water naturally. As I've written in another thread about 'veggie filters', the concept is interesting, can be successful in theory and is wholly impractical for the koi hobbyist. ...BTW, if the idea is to prevent string algae from developing in the pond, Dr Adey's research established that string algae was the best algae for accomplishing nutrient removal in the reef setting. So, how are you going to keep the string algae thriving year-round so it is present and working when the seasonal bout of string algae shows up in the pond? And, it should be noted that in water cleansing facilities that have been established using the adey technology, water hyacinth have proved to be almost as efficient as algae and far less costly to harvest/maintain.

Perhaps someday impracticalities will be overcome and these sorts of things will prove worthwhile in areas where drought prevents reliance on water changes, but I expect the cost and labor will be prohibitive.