Controlling algae.

Controlling algae is an urgent topic. From the following material you'll get an outline of the battle, which is fought along seven main fronts, viz: physical control, limiting nutrients, allelopathic chemistry, the control of light, algicidal chemicals and flocculants, oxidizers including the Clorox Dip, and algae-eaters visible and invisible.
But a certain amount of inoffensive algal growth is natural in the aquarium. So, before algal frustration gets you too wild and violent, read Karen Randall's article "Living with algae" and George Booth's permissive article on algae as friend as well as foe, in a balanced ecosystem that includes various algae eaters. Both are at the Krib.
Physical Control. The systemic controls that follow are all very well, but sometimes the very first step is to get it off the glass. A credit card makes the best algae scraper. Sometimes a handle, as on the Kent Pro-Scraper, makes it easier to manipulate than a plain credit card. And sometimes it just gets in the way. Kent Pro-Scraper has a hard plastic blade, hard enough to remove plaguey green spot algae but not hard enough to scratch the glass. The plastic blade deforms just enough to clean algae out of fine scratches, which will make them less obtrusive--— for a week or so. One thing about a credit card; if the reverse is blank white, any algae spots that you missed on the glass will show up against it, bright and clear. Very useful.

I do use the magnet cleaners. They're especially handy in a tall tank. But I use Flourite in my substrate mixes, and Flourite has so much iron content that particles can get attached to the magnet. If I get too breezy and pick up a minute bit of Flourite or hard quartz gravel, I'm bound to put a serious scratch in the glass from time to time. There's at least one disfiguring scratch in every tank I own. I don't know how you folks with acrylic tanks manage. They sure do look spectacular when they are brand new. But so does a black velvet sofa, eh.
Physical removal of algae involves some plant pruning too.

Nutrient Control. "Algal control is all nutrient control." If your interest in algae just at this moment is basically limited to how to control it, Jeff Dietsch has some very good advice: "Algal control is all nutrient control," Dietsch warns, and though you wouldn't expect to find a simple magic cure for algae, Jeff offers a basic truth that is more helpful in the final analysis: a bloom of algae, like any population boom of one multiplying organism that overwhelms an ecosystem, is a symptom of imbalance in the system. So begin by checking out Dietsch's fifteen helpful tips towards algae-free plant tanks at The Cassi Dietsch Zoo.

Limiting nutrients. The major nutrients of algae are nitrogen, phosphate and potassium, the same macronutrients required by plants. In their competition with algae, the vascular plants have an edge: they have means of temporarily storing excess nutrients, whereas algae are hampered if a nutrient is unavailable even for a brief period of time. This is the gist of controlling algae by limiting one essential nutrient. Paul L. Sears and Kevin Conlin started the discussion; their technique limits phosphate indirectly in planted aquaria by dosing with potassium. The famous "Sears-Conlin article" people may mention, titled "Control of algae in planted aquaria" is archived at www.theKrib.com, where there is a storehouse of algal discussion.
The technique deserves a closer inspection. Though one phase of algal control may be nutrient control, not all nutrients can be effectively brought under control. It's not practical to limit nitrogen, for instance, what with the fish in the aquarium giving off ammonia, and all the decay processes generating more ammonia.
So, what about limiting phosphate? suggest Sears and Conlin. Why can't algae be repressed by lowered phosphate levels? A critic of the method might instance the role of alkaline phosphatase. Though the aquarium's plentiful reserves of organic phosphate generally are unavailable to algae and plants, when mineralized orthophosphate becomes scarce, some algae are able to scavenge PO₄ groups from organic phosphates by using a metabolically costly enzyme, alkaline phosphatase. Alkaline phosphatase is produced in relatively large quantities by planktonic algae in response to low concentration of orthophosphate. It's a negative- feedback buffering system: the lower the orthophosphate levels, the more phosphatase is produced. In fact alkaline phosphatase activity is taken as an indicator of PO₄ limitation in phytoplankton communities.
Algae are quicker and more apt than the "higher" plants to take up phosphate, but, though they they scrounge it faster, they have no mechanism for storing it. So over a period of time (be patient!) the vascular plants will scavenge phosphate and starve algae, the Sears-Conlin technique goes. The major source of phosphate in your aquarium is the fish meal in flake feed, unless you're supplementing it with a phosphate-based pH buffer. So you might want to reduce the amount of flake feed in your fishes' diet, or switch to one of the new lower-phosphate flakes. Phosphate-adsorbing granules, such as Phos-Zorb, can also be added to your chemical filtration media.
Dosing with potassium. An indirect way to assist in this process is to make sure that the third macronutrient, potassium, is always available. Potassium is ordinarily the macronutrient in shortest supply in the aquarium, though not in unpolluted natural waters, it appears. Adding potassium encourages vascular plants to scavenge more of the phosphate that algae need.
Fertilizing. The upshot: what I had been doing in my aquaria has been to add potassium sulfate to the make-up water, at a dosage of 0.5ml/gallon. I did this at intervals, so that the potassium was delivered in pulses. It worked pretty well for me. If I were to dose fertilizer directly to the tanks, I could overestimate the amounts plants were using and build up unhealthy levels. That's why I dose the make-up water instead; that keeps me conscientious about water changes, too!

The potassium sulfate fertilizer I was using also contains some iron. Since there's plenty of iron in my substrates already, and I don't want additional iron in the water column, I've more recently switched to potassium chloride (KCl), which I get at a health-food store in the form of a salt substitute, "Nu-Salt." It also contains less than 1% cream of tartar (more potassium), silicon dioxide and "natural flavor." A literal pinch goes into my 6-gallon makeup water storage cans. I'm told I could also find potassium chloride more cheaply at Home Depot, among the water softener salts.
Residual chloride questions. So the potassium is taken up by plants. Excellent. But what about that chloride ion? Couldn't Cl build up, if my partial water changes weren't enough to keep diluting it out?
A few drops of sodium thiosulfate (de-chlorinator) resolves the issue, apparently. Seachem explain at their website that when harmless sodium thiosulfate-- Na₂S₂O₃-- gives false positive readings for ammonia, it is reacting with the chloride ion that is part of the test reagents, instead of the ammonium ion. After 24 hours, though, according to Seachem, the Na₂S₂O₃ will have have reacted with chloride ions naturally found in water, and will no longer give such false-positive readings.
So an amateur like me can use sodium thiosulfate to react with any surplus chloride.
Jamie Johnson posted at the Aquatic-Plants Digest (23 March 2001) the relevant chemical reaction, which he expressed this way (with my translation):
Na₂S₂O₃ + 4.Cl₂ + 5.H₂O -> 2.NaHSO₄ + 8.HCl.
(Trans. "Sodium thiosulfate plus 4 molecules of chloride plus 5 molecules of water give 2 molecules of sodium bisulfate plus 8 molecules of hydrochloric acid.")
And Na₂S₂O₃ + 2.HCl -> 2.NaCl + H₂O + S + SO₂
(Trans. "And an additional molecule of sodium thiosulfate plus two molecules of that same hydrochloric acid give two molecules of sodium chloride plus a molecule of water, one of elemental sulfur and one of sulfur dioxide.")
Is any fertilizer absolutely necessary? On the whole, plants that aren't being dosed with additional CO₂ rarely need additional fertilizing. Our aquaria are already "eutrophic" compared with natural tropical waters. It's often wise to get the system in balance first, without fertilizer. Once plants are growing modestly and algae are under control, then you can decide what kind of fertilizer you want to add. Go easy, especially on the micronutrients. It's remarkable how many people posting their algae woes on the web forums did not discontinue their fertilizing program at the first sign of an algal problem.

Still, you should know the recipe for PMDD ("Poor Man's Dosing Drops") which you'll find in the same algae-control archives at www.theKrib.com.    ...on the other hand, "Use plants to control algae," recommends Diana Walstad. In her book Ecology of the Planted Aquarium she explains in detail just how the "higher" vascular plants are able to outcompete algae. The old-time fishkeepers did always notice that algae seldom flourished in tanks where the plants were thriving.

Natural Chemistry. Algae fight back. Algae aren't defenseless. Algae have their own ways of keeping the upper hand. Physically, they block light from leaves by overgrowing and directly smothering them. Green water has a similar effect; it absorbs useful wavelengths of light before the light reaches the plants. Another, more subtle weapon in the algal repertory is a metabolical advantage. The algal advantage is this: when carbon dioxide is in short supply, algae are able to scavenge carbon by dissociating carbonates, in a process called "biogenic de-calcification." They do this more efficiently even than a group of plants that have independently developed a similar capability, the so-called "hard-water plants," like Vallisneria. More indirectly, intensely photosynthesizing euglenoids and algal cells in green water scarf up the available CO₂, which has the result of raising the pH. At the higher pH, more free carbon dioxide is naturally converted to carbonate, so that plants are forced to compete for the carbon derived from carbonates, where algae have the edge.
Allelopathic chemistry. "Growing algae produce numerous volatile and nonvolatile organic substances, including aliphatic alcohols, aldehydes, ketones, esters, thioesters, and sulfides," notes the World Health Organization in their guidelines for drinking water quality. Eons ago, the precursors of these allelochemicals probably originated innocently enough as chance byproducts of algal metabolisms.
The extent to which allelopathic chemistry suppresses algae or affects the growth of aquatic plants is controversial. Though allelopathic chemistry is well established in laboratory flasks, it proves hard to establish allelopathic interactions in the comparatively immense volumes of natural flowing waters and large lakes. In a 1998 essay "Shallow lakes, biomanipulation and eutrification", which I'll come back to in a few moments, B. Moss wrote, "The extent to which these substances, faced with a barrage of heterotrophic bacteria, may accumulate and be effective in natural waters on a range of many species of algae which may easily substitute for one another, is unknown and will be extremely difficult to investigate. The potential, however, undoubtedly exists."
An Israeli study "Allelopathy among submerged hydrophytes" by T.H. Shaq was presented as a poster at the IX International Symposium on Aquatic weeds (Dublin 1994). Among five species of aquatic plants tested, Ceratophyllum demersum (Hornwort or "Coontail") and Chara connivens repressed growth and germination of Lemna (Duckweed) and lettuce seedlings.
Diana Walstad credited allelopathic interactions with algae suppression in her book The Ecology of the Freshwater Aquarium, 1999. Ole Pedersen's two-part article "Allelopathy: chemical warfare," first published in The Aquatic Gardener, 2002, (archived at www.tropica.com) was skeptical of Diana Walstad's assertions, especially that when "tanks with heavy plant growth often seem to have very little algae" allelopathic interactions were the cause. Pedersen is skeptical that allelopathic chemistry counts for much in practice, though he does cite sulfur compounds produced by Nitella, Chara and Ceratophyllum spp. that apparently keep the plant itself free of algae by inhibiting algal photosynthesis. Myriophyllum slowly releases phenols that partly suppress enzymes in cyanobacteria. But most toxic phenolic compounds are not released until the plant dies, Pedersen notes, and thus are not technically allelopathy. A quibble, if you're looking at the over-all effect of certain plants in an ecotope. The more relevant studies of allelopathy use intact plants rather than extracts of cellular compounds to assess allelopathy. Pedersen's main conclusion: "Personally, I do not see much ecological relevance in these kinds of experiments. At best, they may be used to look for potential candidates of true allelopathic behavior because the studies, after all, demonstrate that the plants contain toxic compounds. However, many of these studies take the conclusion much too far and recommend using the plants for aquatic weed management or algae control without the necessary documentation for allelopathic behavior in nature."
Would allelopathic effects be magnified in the limited water volume of the aquarium? Some experienced aquarists dismiss the whole subject of allelopathy out of hand. Nevertheless, our confined aquaria seem to me much more like enclosed flasks than they are like natural waters, and I can't see how the lab results could be entirely irrelevant. Allelopathic chemistry is just one among the "buffer" factors that stabilize a planted system and keep its water clear of algae.
Using Pithophora. So a strongly allelopathic alga might also help you suppress other algae, mightn't it? One algal ally that has had some success in this "fight-fire-with-fire" technique is a filamentous alga: Pithophora, or cotton-ball algae, forms big surface mats in still, enriched warm-water ponds in the summertime. It lies on the bottom, until trapped oxygen makes it buoyant. Mine is a sharp lime green, but outdoors Pithophora can be a brownish olive drab and provokes uncomplimentary remarks. In The Ecology of the Planted Aquarium, Diana Walstad reports the test results of A. P. Fitzgerald, who compared guppy tanks with and without Pithophora under 24/7 lighting, and found that the tanks without Pithophora turned green in a week, while those with Pithophora remained clear through a month's trial, even when phosphate and nitrate levels remained high.
My own experience is utterly unscientific, but I find that tanks with some Pithophora are especially free of other kinds of more troublesome algae. Though it's a scourge in sunlit ponds, indoors Pithophora is easily controlled by winding it onto a chopstick or tongue depressor.

Algae do prefer hard water. In general, my soft New York water encourages my lazy fishkeeping habits. But in this soft acidic water I can only culture "green water" by keeping a substrate of crushed coral aragonite to boost the carbonate.

Light Control. About algae and light. At the first sign of excessive algae in a tank, you'll immediately think of adjusting the lighting. There are only three variables in the lighting: the spectrum, the intensity and the photoperiod.
The photoperiod is easy to control. The planted aquarium should be strongly lit about ten hours a day, and not more. So your first move will be to limit the photoperiod with a timer. In the last few years electronic timers have come down in price, so that it's almost a pity to get one of the clunky old mechanical ones with the insertable plastic pins.

The spectrum of light is less easy to control. Algae are more efficient than plants at using light waves in the blue and indigo end of the visible spectrum. "Cool Daylight" bulbs may encourage algae less than "Gro-Lux" bulbs, which are strong in red and blue sections of the spectrum. "Warm Daylight" bulbs put out intense light in the parts of the spectrum to which the human eye is most sensitive; though they may look brighter, they are not brighter in the parts of the spectrum used for photosynthesis.
The intensity of the light can be defined as the output (not wattage) times the square of the distance. Concerning the intensity of the light, I find that I'm always being given conflicting advice, viz:

"Don't reduce the intensity of your light--— that is, the wattage times the square of the distance from the water surface--— to control algae," says Team A. Algae can get by at lower light levels than "higher" plants. In other words, the photosynthesizing plastids embedded in each algal cell become saturated at a lower intensity than the comparable plastids in plants. Intense light, like sunlight, also has an inhibiting effect, the A Team pros tell me. Algae are photoinhibited at levels that vascular plants can still use. And diatoms ("brown algae") are photoinhibited at the lowest levels of all. But frankly I can't imagine being able to flood my tanks with so much artificial light that algae are genuinely photoinhibited. Instead, I'm noticing that a densely-planted tank I have, which receives a couple of hours of natural sunlight each day, has clearer water than any of my tanks that depend entirely on artificial light.

"Do reduce the intensity of your light to control algae," says Team B. Intense light can make iron more available for algae and plants, in a process called "photoreduction." Iron's increased availability under intense lighting is a prime suspect for algal stimulation, rather than the intensity of the light itself. (There's lots more detail about "iron photoreduction" in the aquarium in Diana Walstad's book, Ecology of the Planted Aquarium, 1999, pp 167-169.) I've noticed that problem algae can slowly become an issue as a fluorescent tube ages; the spectrum of its output may be shifting in a way that encourages algae. The remedy can be as simple as installing a fresh bulb.

Algicides. About algicides. Forget the poisons. There are some ineffective and dangerous ways to "nuke" algae with poisons, but you should ignore them. Water additives formulated for pond use and touted to kill algae generally contain simazine or copper, or both, drugs that are too toxic to fish and plants and too difficult to control for them to be recommendable within the confines of an aquarium. Too fine a line distinguishes a dosage of simazine that will kill algae from one that will shock the higher plants into a slow irreversible decline. Distributors have changed their tone from "may affect plant growth" to limiting recommended use to fountains, ponds and aquaria "containing no live plants." The shock to plants simazine causes won't show in the first days, by the way.

Since a simazine-based algae-control product still being marketed to pondkeepers is touted as containing "EPA-registered" ingredients, it's worth following up at the official Environmental Protection Agency website. where you can also do a search for "simazine" in order to see how the E.P.A. actually does "register" simazine. I discovered at the site that it's a pre-emergent herbicide that doesn't bind to sediments nor evaporate; in fact it's persistent for "a few months to a few years," rather a long time in an aquarium. In 1992 Ciba-Geigy voluntarily withdrew the registration of simazine from all aquatic uses: aquariums, ponds, fish hatchery ponds, ornamental ponds, ornamental fountains, and swimming pools, and informed formulators that support for these uses was being withdrawn. Simazine is one of the herbicides called triazines that have been under an EPA "special review" since 1994. DuPont (apparently sensing the direction the wind was blowing) agreed to phase out its proprietary triazine, called cyanazine and marketed as Bladex, by the end of 1999, though they didn't want to connect their action with studies implicating the chemical in cancer or studies finding that it was showing up in drinking water supplies in heavy agribusiness areas like the Midwest. Other agribusiness lobbying has kept simazine and other triazines on the market, for now. Back in 1986, before these reservations surfaced, Neil Frank published an article on the action of simazine, the gist of which is archived at theKrib.com. If you're considering using simazine to control algae, read Neil Frank's article.
Polyquat. A less-destructive successor to simazine is "polyquat," a polyquaternary ammonium compound: (poly [oxyethylene (dimethyliminio) ethylene (dimethyliminio) ethylene dichloride]), with an E.P.A. est. no. 8709-PA-1.
Polyquat is widely used as a swimming-pool algicide and in clearing industrial cooling-water systems. It is a surfactant that lowers the surface tension of the water and "wets" algal cell walls, splitting their delicate membranes and spilling the cell contents. Polyquat is manufactured by Buckman Labs, Memphis TN, and repackaged for the aquarium/pond market.
After testing their polyquat, "Pond Care AlgaeFix," with pond plants, including Cabomba and "Egeria" (Elodea), Aquarium Pharmaceuticals marketed "AlgaeFix" for aquaria in 2001. They warn you, at their website, not to use AlgaeFix with any crustacea you care about, like freshwater shrimp and crayfish. Crustacea that you don't care about, copepods especially, will also be decimated by polyquat: if your algicide kills off your algae-eating plankton, can it be a good thing in the long run?
Swimming pool owners who require brilliant clarity keep their water "dosed up" with polyquat. "One treatment with PolyQuat can last months," says the PoolStore website approvingly; one dose of polyquat in an aquarium may also not degrade for months, and in an aquarium, that's a long long time.
Even an amateur has reservations about adding any surfactant to aquarium water. And not every professional would agree that polyquat is harmless to fish. "This pesticide is toxic to fish," warns the Nu-Calgon Material Safety Data Sheet. "Keep out of lakes, streams or ponds." ...I'd add "or aquaria," but you know how skeptical I am...
Swimming pool owners eliminate the dead algae with either a shock dose of chlorine or some other oxidiser to break them down. They may thenuse a flocculant "water clarifier" to clump them together to be caught in the filter
About flocculants and green water. Flocculants appeal to your worst "nuke it!" instincts. A flocculant is a substance that makes colloidal silt and organic particulates, including single-cell algae and even bacteria, clump together in "flocs" and precipitate out of the water column. Flocculants are an aspect of chemical filtration. Typical "clear water" flocculating products often take a synthetic polymer built of a long chain that bears many positively-charged sites and combine it with a polyvalent (multiply charged), non-toxic metal salt, such as alum (aluminum sulfate). Kordon gives an unbiased account of how their flocculant "water clarifier" Trans-Clear works, at their website.

It would be so nice to be able to unconditionally recommend a flocculant. Why can't I? Overdosing with a flocculant water clarifier can temporarily cloud the water with colloidal particles, but this is more an issue for the aquarist than for the fish, which are unharmed. But the flocculants carry strong positive charges, which unselectively bind with negatively-charged sites. Negative charges on small particles make them mutually repellant and help keep them in circulation. The cellular membranes of algae cells also carry negative charges, so the flocculant works like a charm! But mucus-covered gill surfaces carry negative charges too; they can't bind to the flocculant, so if you overdose, the flocculent may bind to them, gumming together the delicate gill filaments. If you eschew aloe vera as a stifling gill glue, you'd also be cautious when using a flocculent. Small fishes are rumored to have been directly smothered by overdosing with flocculants. I'm convinced flocculants are stressful.

But the basic point is that both poisons and flocculants are piecemeal panic measures; if you haven't got conditions in the aquarium balanced, algae will be back.

Oxidizers and the Clorox Dip. Oxidizers like potassium permanganate or hydrogen peroxide occasionally still get recommended for algae control. George Reclos' excellent article on using a syringe of 3% hydrogen peroxide, just as it comes from the bottle, in vanquishing black brush algae, with some ravages to the plants, is archived at the Malawi Cichlid Homepage. He tells you specifically which plants were most and least affected. His sharp-focus closeup pix illustrating his article are outstanding.
Read up on these oxidizers here in the "Health & Diseases" folder as well, and see if you would want to subject your fish to a dose strong enough to affect algae.

Sometimes a massive die-off of algae can release toxins into the water. Be cautious and do water changes before and after any anti-algal treatment. You might want to add fresh carbon into the filter media too.

The Clorox dip. Clorox (household bleach-- a solution of sodium hydrochloride) also works by oxidation. Individual plants that can be removed from the tank can be rid of persistent algae with a Clorox dip. Try a word search "Clorox dip" at the Aquatic-Plants Digest. (Say, isn't this exactly the kind of insider stuff you always hope to pick up by lurking at the Aquatic-Plants Digest?)
A dip using a 1:20 solution of Clorox in tapwater for two minutes will kill even the most ineradicable tufts of hair algae attached to plants. I hope it wouldn't even occur to you to take a "short cut" and try this right in the aquarium. Please use a kitchen timer. Remove the plant after two minutes, willy-nilly. Don't expect the algae to detach and vaporize right there before your wondering eyes. If the technique hasn't worked after a week, you can always try it again later. Treated plants should be rinsed in water with some de-chlorinator (sodium thiosulfate) added, to neutralize any chlorine before they return to the aquarium. Plants like Anubias, which grow a protective waxy cuticle even on submerse leaves, are more resistant to a bleach treatment than soft-leaved plants, like Echinodorus or Cryptocorynes, which can be badly savaged by a Clorox dip.

Java Moss is especially sensitive to this treatment; instead of passing it through the Clorox dip, I just rinse Java Moss, when it gets choked with cyanobacteria and algae, and put it into a glass of water straight from the tap and set it in the dark fish cupboard for five days. Each evening I renew the chlorinated tapwater. The first couple of days the contents of cyanobacterial cells stain the water blue-green. After five days of constant darkness and mild tapwater chlorination, the cyanobacteria and algae are gone and the strands of Java Moss are clean.
Blackworms are great at cleaning Java Moss too. If you keep blackworms, strands of Java Moss infested with algal coatings can be dropped into the blackworm pan. Three or four days later the blackworms have stripped the moss clean and you can drop it into a tank, where fish will be glad to separate the blackworms from Java Moss for you.

Some other moss-related ("bryophyte") aquarium plants, like Naias and Ceratophyllum (Hornwort), are also particularly sensitive to bleach.

Vigorously-growing stem plants ("bunch" plants) outgrow algae. Don't bleach-dip these, either; you'll just set them back, and then algae will overwhelm them. Instead, just pinch off the growing tips with a few algae-free inches of growth. Float the good tips and discard the remainder.

Paul Krumbholz' brief notes on the bleach dip for eliminating hair algae, and some pointers for encouraging plants' rapid recovery afterwards, are posted at aquabotanic.com

Algae-eaters visible and invisible. If your green meadow were growing tall and rank, rather than using a flame-thrower you might turn the sheep out to graze. Besides the visible algae-eating fishes and invertebrates, there are a host of microscopic grazers in the plankton and among the biofilm. Encouraging zooplankton is really what keeps the water clear and algal films under control.

About "algae-eaters." Certain fish have an appetite for algal films and over-mature plant material that's going soft. (Certain fish have notorious appetites for un-softened plant leaves, too.) Each species has preferences. It generally takes more than one kind of algae-eater to control the full range of algae in a tank. Your experience will show you which combinations of species are competitors for similar kinds of algae and which complement one another in their algal tastes. The SAE, or Siamese Algae-eater, is Crossocheilus siamensis. It has some attractive but less useful Epalzeorhyncos relatives plus an oafish imitator, the "Chinese" Algae-eater, Gyrinocheilus aymonieri, which you may want to avoid. The algae-rasping Otos, various Otocinclus spp, are very helpful and endearing miniature Loricariid catfish. Many other Lories (Loricariid catfish) depend on algae, especially the young ones. But as they grow, the larger ones, like the Common Pleco, lose interest in algae and start mindlessly trashing plants. Lately folks have embraced the slightly snappish and aggressive cyprinodont, Jordaniella floridæ, the American Flagfish. I have no personal experience with it. Many other herbivorous fish, and omnivores such as Barbs, will pick pick pick among the algae all day long, without having much effect on it, however.

About algae-eating shrimp. Takashi Amano introduced us to shrimp for the freshwater aquarium. He is convinced that algae are being kept under control in his immaculate, richly-planted tanks by algae-eating shrimp, which he chose after an exhaustive selection process he described in one of his books, which reminded me of the next-to-last chapter of Cinderella. Surely Caridina japonica, the "Amano" shrimp, are supporting themselves on algae and detritus, and preferentially on any available flake feed, it appears, but I think it's the vigorously-growing plants that outcompete algae in Amano-style aquaria. Planted aquaria like Amano's always have plentiful algae-eating plankton life too.
I wish genuinely tropical shrimp from freshwater habitats, rather than shrimp that really need fairly cool brackish waters to thrive, were consistently offered at my local LFS. They aren't yet. But you'll find what information I have about shrimp among "Invertebrates" rather than here in the Algae Combat Zone.

This technique has been developed especially at the IACR Centre for Aquatic Plant Management, Sonning, near Reading, Berks. There's an information sheet at www.aquabotanic.com (click to the Library). Investigators at McGill University interested in sustainable farming practices picked up the U.K.'s Aquatic Weeds Research Unit hypothesis.

On the other hand field trials in New Zealand in 1994 were inconclusive, even finding enhanced growth of "water net" algae in the early stages of the trial. In the most successful lab trial (no. 2) "it was found that the decomposing straw had consumed all available nitrogen in the water." That seemed like a suggestive observation to me.
Barley straw has also been successful in keeping garden ponds and koi pools free of greenwater algae. Robin Rhudy has had success with barley straw clearing her pond. At her website, she has assembled barley straw links, including suppliers of barley straw extract.
However, the explications of how barley straw works often verge on alchemical fantasy, viz:

"As barley straw decomposes in water, it releases lignins. These are oxidized to humic acids in the presence of oxygen. If sunlight then shines on the humic substances, hydrogen peroxide is formed. The peroxides in turn inhibit the growth of algae. They have no effect on existing algae. Because hydrogen peroxide is dangerous in high doses and is highly unstable (it does not last long), adding hydrogen peroxide directly to the water would not work and could harm the animals and plants. Straw releases a constant supply of low levels of hydrogen peroxide which is safe and effective. You would have to sit by the pond and add a drop of dilute hydrogen peroxide every hour or so to get the same effects."

If the science of it all seems rather soft and murky, the business aspect of it all is neither soft nor murky. A report in the Pittsburgh Post-Gazette's web version quotes Wayne Davis, president and CEO of Plantabbs Products, a Maryland-based firm.

"His business has been experimenting with barley straw for several years. Davis, a water lily grower, says he approached this cure with much skepticism. But he says it works. In fact, his firm imports and sells Scotch barley straw, a high-quality straw left from the production of Scotch whiskey. He sells half-pound bales of straw, in mesh netting with one weight, for $24.95 plus shipping. So why go to the expense of buying special barley straw? According to Davis, his firm has experimented with all kinds and nothing seems to work as well as the straw from barley used in the whiskey industry."

Maybe you should run a word search for "barley+straw" at www.google.com and judge for yourself.