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Living With Algae . . .
Since You Can't Get Rid of It

by Karen A. Randall <76535.2776-at-compuserve.com>

I have had a number of conversations with various members in the past few months about algae problems. In fact, this subject came up so often on the Home Show tour, that Lee Finley laughingly suggested that we devote an entire issue of "The Daphnian" to the subject, or at least form a new study group, (Algae Growers of America?)

Well, for those of you who are members of the Aquatic Gardeners, you know they beat us to it. They recently published an issue almost competely devoted to articles on algae.

Here, then, is the distillation of what I've experienced, read and surmised about some of the many forms of algae.

I categorize algae in two different groups, better and worse. Under the "better" category, I place many of the true green algaes; the ones that have the same requirements as higher plants, and cannot be avoided (although they may be minimized). In the "worse" category are all the others, such as, blue-green (cyanobacteria), brush, beard, brown, (diatoms) and free floating algae.

Let's deal with the "better" algae first. This is the equivalent of weeds in the garden. It is not possible, or even desireable to completely avoid this type of algae. There are algae spores in the soil, in tap water, and even in the air.

The trick is to keep the algae from getting the upper hand while allowing the higher plants to flourish. To do this, you must make sure you are meeting all the needs of your plants, while leaving very little in the way of excess nutrients for the algae.

Plant your tank heavily from the very beginning with fast growing plants. Fortunately, fast growing plants are also very often inexpensive, so don't skimp. You can pick up large bags of Water Sprite cheaply at the monthly auction. This is just what you need.

Make sure your plants are supplemented with trace elements, but keep nitrate and phosphate levels in the tank as low as possible. Do not over stock the tank with fish, and do not over feed. Make sure you are doing hefty water changes on a frequent basis.

Finally, make sure your lighting is in balance with the nutrients and CO2 available in the tank. As a rule of thumb, unless supplementing with CO2, you should be using a minimum of two full length flourescent tubes over each tank, with a photoperiod of approximately 12 hours. If you know the nutrient levels in your tank are low, and you experience a bloom of green algae, cut the light back slightly. If you get brown "algae", (diatoms) increase the light slightly. If you are using CO2, you can (and should)use lots more light.

Now that everything is balanced, you should be home free, right? Sorry to disappoint you. You will still have algae. You will have to deal with what we'll call "normal" algae growth exactly as you would weeds in the garden. If you've ever tried an herbicide in the garden, you'll know that it kills most other plants as well as the weeds. The same is true of algacides. Don't believe the bottle. The plants may look fine a few days after the treatment, but damage can take a long time to become visible. Generally, the slower growing plants will take the longest to show damage.

Normal algae must be removed manually, either by you, or your fish. Lets start with the possiblities among the fish world. Mollies are great at algae removal. The problem is that they do best in brackish water, which is not good for your plants. Some people keep them successfully in straight fresh water, but I haven't had much luck keeping them that way. There are a number of sucker mouth catfish that can be used. Avoid the larger "plecos" because they can do a lot of damage if they go on a rampage (most do from time to time). Some people swear by Ancistrus sp., but they may dine on tender plants once the algae supply dwindles. Pecoltia sp. are safe for the plants but don't eat a lot of algae. Otocinclus sp. are always safe, but you'll need a lot of them. My personal choice is either the Flying Fox (Epalzeorhynchus kallopterus), or the Siamese Flying Fox (E siamensis). Both of these will eat quite a bit of algae, and never damage plants. Both get a bit territorial as they grow. The Flying Fox is worse, but it is also prettier and more readily available. I find that if you keep several, and your tank is at least 4' long, their aggression is directed mostly toward each other, and limited to the occassional split fin. Another popular choice is Farlowella sp. or "twig" catfish.

O.K., the clean up crew is in place, but what if they still can't keep up. Algae can get out of control at times when your nutrient/light/CO2 ratio is out of balance, or if plant growth is retarded. This can happen in a newly set up tank where plants are still settling in, or as a result of medications or other chemicals being introduced to the tank.

Now it's time for you to get to work. Obviously, you will be scraping algae off the glass as part of your regular maintenance routine. Many people say not to bother trying to remove algae from plant leaves. They contend that algae will only grow on dead or dying leaves. In my experience, this is true in a properly balanced tank with CO2 supplementation. However, in tanks without CO2, I have found it worth while to remove soft algae growth from the large leaves of slow growing plants such as Anubias sp. and Java Ferns. Use your judgement. Small leafed plants choked with algae are not worth the trouble. With these, divide out a clean section to replant, and throw the rest away. Filamentous algae of various types can be removed by winding it around a toothbrush.

"Worse" algae many get started in a tank due to poor water quality. If there is any question about the cleanliness of your tank water, fix this problem before bothering with anything else.

If water quality is not a problem, and your tank is properly balanced, it is possible that your tap water contains phosphates. In this case you will need to use some filtering system, chemical or R.O. to remove the phosphates. Otherwise, it will be very difficult to solve an algae problem. Other sources of inadvertent phosphate addition are buffering chemicals, water conditioners, rook wool on potted plants, and some plant fertilizers (even those meant for aquariums!)

Here is a sampling of various "worse" algae types, and the best ways of dealing with them.

Brush Algae

This algae (actually a "red" algae even if it doesn't look that way, is usually dark grey, sometimes silvery. It grows in tufts on the edges of large plant leaves, and on decorations and equipment. It is difficult to remove manually. Its presence is almost always a sign of high nutrient levels in the tank. It will often disappear spontaneously when water conditions have been improved. High iron levels have also been implicated in the proliferation of this algae. Siamese Algae Eaters are said to eat this algae, but they are the only ones who will!

Blue-Green Algae

This is actually a cyanobacteria. It comes in many (sometimes lurid) colors, but is characterised by it's slimy texture. It is easily dislodged, and rolls off in sheets. It often gives the tank an unmistakable swampy odor. Blue green algae can fix nitrogen, so low nitrates and clean water will not stop this horrible stuff. Left unchecked, it will suffocate the plants. I don't think anything will eat it. It is most often a problem in tanks with high pH and alkalinity. The good news is that there is a cure! 200 mg of erythromycin/ 10 gallons of water will kill it, usually over night. Altough the label says that the biological filter will not be affected, be very sure to track ammonia and nitrite levels in the tank if this method is chosen and be prepared to do water changes to reduce these levels if needed.

Green Water

Also known as an "algae bloom", this irritating phenomenon frequently occurs in a newly set up tank, or as the result of a major upset in the biological filter in the tank. Even massive water changes will only temporarily improve the clarity of the water. Given time and good water quality, these blooms usually disappear as mysteriously as they began, but if you don't want to wait, here are a couple of options to try. I have had good luck on several occassions by simply turning the lights off for a week. This seems to be enough time to kill the algae, and while it may set plant growth back a little, it does not seem to do any permanent harm to the higher plants. Another method is to introduce a large number of daphnia to the tank. Thetheory is that these will eat the free floating algae cells, and will, in turn be eaten by the fish. This sounds like an elegant solution, but it's one I haven't tried personally.

Brown Algae

Brown algae are actually diatoms. They settle on most surfaces, but can be easily brushed off manually. The presence of brown algae is common in a newly set up tank at about the one month mark. If this is the only reason for the occurrance, it should abate on its own within a few weeks. A good sized group of Otocinclus will clear every surface of this type of algae in the course of a weekend.

In an older tank, the presence of diatoms usually signals a deficient supply of light, and or high levels of silicate. The problem can usually be remedied by carefully increasing the lighting on the tank. If lighting is not the problem, the other possibility is an excess of silicates in the water. These can be removed using a silicate adsorbing resin in your filter.

It has been suggested that you can prevent the introduction of unwanted algae spores into your tank by sterilizing new plants in a mixute of one part bleach to 19 parts water for two minutes. The plant should then be rinsed thoroughly and immersed in water containing a chlorine neutralizing solution. I personally have not gone to this extreme. I prefer to look over prospective plant purchases carefully, and buy only specimens that are clean, robust and healthy.

Don't get discouraged by algae. Remember that if you keep your water quality good, and provide the best possible conditions for your plants, the plants will out compete the worst of the algae. As for the algae that does turn up anyway? It's time to start weeding!


This article was originally printed in The Daphnian, publication of the Boston Aquarium Society as monthly instalments of my column, ``Sunken Gardens''. BTW, the column was voted ``best column'' in the North East Council of Aquarium Societies in both 1993 and 1994.
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This page was last updated 29 October 1998