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Aquarium Algae Information

Last Updated: 4/18/12

Algae and Algae Cleaning - includes species of algae-eating animals
Lighting, Relationship to Algae Growth, and Fish Sleeping
Ornament and Plant Cleaning
Cloudy or Green Water

Algae and Algae Cleaning

There are two main algae cleaning options. The first is to physically do it yourself with algae pads and scrapers. If done every week, this is no big deal. Left to fester, the algae is nearly impossible to remove. The other option is algae-eating fish or snails. These include many species of plecostomus, otocinclus, Siamese algae eaters, and even mollies and rosy barbs. Ramshorn, trapdoor, and mystery snails will eat algae too.

Snails, shrimp, plecostomus, and otocinclus:

Ramshorn and trapdoor snails are good algae eaters. Apple, golden Inca, three-horned, and pond snails will eat some algae but will also eat most plants you might have. For information on snails, go to my snail page. Some shrimp may eat some algae as well. Visit my shrimp page for more information. When keeping any algae eater, be sure to have supplemental foods (cucumber, kale, algae tablets, etc.) to provide when there is not enough algae. Also, be aware of their potential sizes and compatibilities with your other fish. For information on three groups of algae eating catfish, visit my common plecostomus page, bristlenose plecostomus page, and my otocinclus page.

Siamese algae eaters and kin:

Siamese algae eaters are one of the best algae-eating fish, especially for planted tanks. Flying foxes look very similar but their fins have black marks and white tips while those of Siamese algae eaters are clear. For information on Siamese algae eaters, false Siamese algae eaters, Chinese algae eaters, and flying foxes and how to tell them apart, check out my algae eater page and this site. Siamese algae eaters are reported to eat brush algae (hair algae).

Other fish:

Rosy barbs, cherry barbs, and American flag fish are reported to eat some hair algae. Rosy barbs and flag fish are prone to nipping and are best used to clear up a tank of hair algae before putting other fish in it. (I added two rosy barbs to my hair-algae-infested 50 gallon tank in 2002. They got along okay with the other fish. A year later, and there was no hair algae and 30-some barbs!) Some cherry barbs, but not all, seem to like to eat some algae as well. I recently have been told about the coldwater fish Garra pingi pingi which is a good algae eater, hard to find, but may pester other fish. Also, Frank at Frank's Aquarium sells a new sort of algae-eating sucker-type fish (not a catfish).


I have not mentioned using chemicals to kill algae. Most chemicals will kill most plants and may even harm the fish. I never use algicides. I do occasionally use a product (AccuClear by Aquarium Pharmaceuticals) which is a polymer which causes algae to clump in my pond. It causes less harm but is only a short term solution; in fact, it only increases visibility an inch or two if the water is very filthy. I use it to get a foothold of clarity in a tank that is cloudy due to things like being stirred up.


In ponds and large tanks, UV sterilizers (see here for information) can be used to kill suspended algae (and anything else alive that goes past it).
Providing higher plants in large quantities in both aquariums and ponds also provides competition for nutrients and results in less algae.

Barley straw is widely used in ponds as a natural method to control most types of algae. See the barley straw page for more information. I tried some barley straw in a mesh bag in my 20 gallon's filter to see if it helped to control hair algae. I added it on 3/17/01. When I tore down the tank to move fish on 6/16/01, the hair algae was still a problem. Update 9/15/03: I have bags of barley straw in all my tanks. Right now, there is no hair algae.

For information on types of algae, ways to prevent algae, how to remove algae in a pond, and UV sterilizers go to my pond algae page. Also, see the next sections for more information on algae.

Lighting, Relationship to Algae Growth, and Fish Sleeping

Types of lighting:

My fish tank lights are on from about 7:00 am to 6:00 pm. I do not vary this during the year although that is often a good idea, especially to initiate spawning. The natural sunlight extends the fishes' days during summer to provide seasonal changes. Fluorescent lights are best unless you want a ton of plants or saltwater tanks with corals. Incandescent lights are only good short term or specifically to add heat (like for lizards). I do not know enough about halogens, metal halides, etc. to speak about them so you need to contact professionals in those areas for information. These and even newer lights provide more light in less space for thriving large freshwater plant tanks or saltwater tanks with invertebrates and macroalgae.

Light cycles and fish sleeping:

If you do not have algae eaters, you should only have the lights on for about 8-11 hours with less light yielding less algae (assuming no direct sunlight). If you have a hungry, large plecostomus to feed or a lot of small algae eaters, you should keep the lights on for 10-13 hours a day. Less than about 8 hours a day (unless there is a lot of natural light) or more than about 14 hours will confuse the fish. Yes, fish sleep! They lay on the bottom, in plants, etc. during the night if diurnal and during the day if nocturnal. Diurnal fish need to be in the relative dark to sleep well just like most humans. Nocturnal fish will not forage and be active unless it is relatively dark. Most fish cannot block all light from their eyes since they have no true eyelids but some catfish can block out light with adapted omega iris' (plecostomus for example), and others (cories for example) can blink their eyes. Fish woke from sleep by bright light often dart around in panic and may injure themselves.

Ornament and Plant Cleaning

New plants can be treated to kill snails, algae, and any fish parasites or bacteria. First, remove any large snails, algae clumps, etc. Then, inspect them for problems and remove any dead leaves. To kill animals and algae, plants can be soaked in alum, potassium permanganate (KMnO4), or a 1:20 solution of bleach to water. Only soak for about two to ten minutes in a bleach solution depending on the species or the plant will die too (see below for precautions and notes). Soaking plants in about 0.4 Tablespoons of KMnO4 per gallon or about 15 mg/L should disinfect them. Doses for treatment of fish must be much lower. I do not know the recommended dose of alum. After soaking new plants in dilute bleach for 10 minutes, I then soak them in fresh water with dechlorinator added for another 10 minutes. Then, they can be rinsed and put in the tank. It is recommended that you remove any ties around the plant (lead weights, etc.) or containers but I sometimes leave the weights on to keep the fish from uprooting them (as often). Gently insert the plant into the gravel.

Ornaments and fake plants can be cleaned by soaking in a ~1:20 solution of bleach to water for a few hours or as long as needed. Then, soak in fresh water with dechlorinator added. I also soak entire tanks in dilute bleach between uses.

Precautions of Using Bleach to "Treat" Live Plants:

Soaking plants in a 1:20 solution of bleach works well for tough plants with thick skins like most anubius, crypts, onion plants, etc. It does not work so well for fine leaved plants or sensitive plants in that it can either outright kill the plant or cause it to yellow or drop its leaves (from which it may recover eventually). I have found that hornwort is very sensitive to bleach and should be treated via another method or dipped for only about two minutes. In a 10 minute dip, hornwort will drop all of its leaves and rarely recover. The leaves on anacharis will turn yellow and fall off it dipped for more than 10 minutes or in too high a concentration. In many cases though, the plant will eventually grow new leaves. Anacharis should only be dipped for about 5 minutes. For other plants, I am not sure how they will react. If the plant is too valuable to risk it, then stick with safer KMnO4 dips or forgo the treatment (and perhaps add snails or algae). Note that with shorter dips to spare the live plants, it also may spare any of the snails, algae, or bad things you are trying to kill.

Cloudy or Green Water

A frequent question of new aquarists is why their newly setup tank turns cloudy. There are many possibilities to consider. Either something is growing (bacteria if white, algae if green), something is being added (bad water, too much food, too many fish and their wastes), or something is leaching (gravel, ornaments, driftwood). In any case, it is a good method of attack to change 30-50% of the water every few days until the water is again clean. Adding fresh carbon may also help. Without diagnosing and treating the cause, however, the problem will return. Some reasons that water may be cloudy in a newly setup tank and solutions include the following.

1. The gravel was not properly rinsed. Remove the gravel and rinse well.
2. The gravel or other ornaments contain limestone or other leaching materials. Remove the offending materials.
3. Driftwood was not properly treated and is leaching. See the driftwood section for driftwood treatments.
4. Bacterial blooms are common in new tanks and make the water appear milky. Change 50% of the water every few days until water clears up. Add liquid bacteria to help the good bacteria out- compete these bacteria. Bacterial blooms are often fed by excess fish food and fish wastes but many also be common in certain tap waters high in these bacteria or the foods that they like. See my water chemistry page for more on bacteria.

Green water is usually caused by suspended algae. See this page and my pond algae page for information on dealing with suspended algae. Short term, do frequent large water changes until the problem subsides. Usually the cause is exposure to too much sunlight or artificial lighting coupled with too many fish, excess fish food, and/or fish waste. Correcting these problems should alleviate the green water.

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Go to the main plant page (full index).
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See the master index for the plant pages (quick index).

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