1 of 6

Write now Article Tools

There are three basic types of aquarium algae: true algae, protists, and cyanobacteria, which used to be called blue-green algae, causing much confusion to this day. One must know which type is growing in order to determine the proper response.

In a well-lit aquarium of neutral-to-acid pH, heavy planting tends to suppress the growth of all three types, as higher plants can outcompete them for nutrients. CO2, iron, and magnesium are common limiting nutrients, deficiencies of which may cause unacceptable algae growth. Consider bubbling yeast-produced CO2 into the aquarium, planting in a laterite or fluorite-supplemented substrate, and addition of aquarium fertilizer drops will help the plants stay ahead of the algae.

Protists such as diatoms ("brown algae", which clouds the water and forms a film on the glass) and Euglena (said to be the main culprit in "green water" tend to flourish in new aquaria with an incompletely established biological filter, as they out-compete the bacteria for ammonia, nitrite, and nitrate. Reducing the lighting intensity or duration tends not to help, as these organisms flourish in low lighting. Diatoms thrive at high silicate-to-phosphate levels; new aquarium glass and some substrates are known to leach silicate for several weeks after setup. Establishment of the biological filter bed and the end of silicate leaching tends to eliminate this problem. Planting the aquarium before protists take over is the best prevention; adding Atyid shrimp, Daphnia, Cyclops, or other filter feeders will eliminate it after it starts. Reverse osmosis or treatment with adsorption resins should be considered when tap water has high levels of silicate.

Cyanobacteria are perhaps the most obnoxious and difficult to control once they take hold in the form of dark slime or slimy, hairy tufts on plant leaves and driftwood. Moreover, they are nitrogen-fixers, thriving, once they take hold, in aquaria with low nitrate levels, and poisonous to algae-eating fish and invertebrates. Improved water circulation and thorough testing for excess nutrients may help to eliminate their growth, but often the best course of action is treatment with antibiotics. Erythromycin (trade name "Maracyn") tends to not disrupt biological filter beds in freshwater aquaria, but will kill most aquarium cyanobacteria; if the infestation does not respond, other, more disruptive antibiotics should be considered.

While protists and cyanobacteria tend to be transient problems, true algae are persistent and should be considered permanent aquarium dwellers, to be managed, not eliminated.

Black beard algae, a species of red algae, grows in aquaria, can use the bicarbonate ion as a carbon source and grows in aquaria with high carbonate hardness. Lowering the KH may cause it to diminish; if high KH is not the cause, if lowering is not an option, or if the remedy fails, consider adding siamese algae eaters (Crossocheilus siamensis) or Jordanella floridae, both easy to keep, and both known to eat black beard algae.

Several forms of green algae also commonly infest aquaria. Spirogyra, green beard, and similar filamentous algae are readily eaten by most algae-eating fish (Otocinclus, flying fox, Poecilla, etc.) and shrimp (Cardinia, Neocardinia, etc.) and snails, but will grow to unmanageable levels if phosphate concentrations are out of hand. If the shrimp, snails, or fish can't keep up, consider adding a phosphate-adsorbing sponge or resin bag to the filter. Hard spot algae grow on glass, rocks, and the leaves of slow-growing plants. While not problematic, on the glass they may block views. Plecostomous fish and snails will eat some of these algae, but the most effective response is mechanical removal with a razor blade.

Learn more about this author, Bennett Kalafut.
Click here to send this author comments or questions.

Add your voice

Know something about Fixes for fish tank algae?
We want to hear your view. Write now!