Algae Problems

The large majority ofaquarists have found themselves confronted with undesirable levels of algae that are sometimes difficult to combat. Generally speaking, it is better to avoid excess growth in the first place than to have to try to fight it- often with varying degrees of success.


This overgrowth can be recognized by its greenish or yellow-brown color, (while whitish or gray filamentous masses, made up of bacteria and fungi, may also be mixed in with algae). This type of growth can form quite thick layers on the glass panes, the bed, and the decor, appearing as filamentous tufts or even completely covering other green algae. While a modest presence of algae can be considered a sign of equilibrium, this overgrowth is evidence of a degree of imbalance, and so algae are often referred to as biological indicators. You must be careful, however, as every aquarium is a special case, and applying a generalization to a specific situation could ultimately lead to the wrong conclusions.

The disadvantages of algae

Apart from being an eyesore, excess algae grow on the panes, reducing the visibility. They attach themselves to plants and proliferate, with the subsequent risk of suffocating their hosts, as the plants are prevented from exchanging gases and absorbing the salts in the water. Finally, they incrust themselves on the slightest details in the decor, which does nothing to enhance the visual effect.

... and their advantages

These are substantial. Algae consume nitrogenous substances, particularly nitrates, and sometimes ammonia. This is the normal role of plants in fresh water, and algae can therefore complement this action or, on the contrary, exert an antagonistic effect by diverting nutritious salts away from the plants. The vegetation is less abundant in marine tanks, and so algae - particularly the filamentous green ones - can play an important role.

• If due care is not taken, micro-algae can rapidly cover the decor and panes of an aquarium. This does not necessarilyhave a negative effect on the fish, but the visual effect is seriously undermined.

Algae can also be grazed or ground by some fish. In fresh water, this applies to the Poeciliids and the species known as "suckers" or "washers" (Gyrinocbeilus, Ancistrus, Hypostomus, Panaque, Oto-clinchus, Epalzeorbynchus). In sea water, algae form part of the diet of fish families, such as the Chaetontids, Centropyges, and Acanthurids; their presence in an aquarium can help these fish acclimatize themselves to the artificial environment of the domestic aquarium.


Mechanical methods

Algae can be removed by hand, by sliding the leaves of the plant between the thumb and index figure, by rolling filamentous algae around a stick, or, finally, with a scraper equipped with a razor blade or a small scouring pad (available commercially, although you can also make one yourself). Any rocks, sand, coral skeletons, branches, or roots infested by algae can be treated, outside the aquarium, in a 10% bleach solution, to which these algae

• If due care is not taken, micro-algae can rapidly cover the decor and panes of an aquarium. This does not necessarilyhave a negative effect on the fish, but the visual effect is seriously undermined.


Red algae (Rhodophyceae)

It is unusual to find a proliferation of these algae in an aquarium. Brownalgae (Pheophyceae)

In an aquarium, these mainly consist of diatoms, unicellular microscopic algae. These grow and form a thin film on the decor and glass panes of the tank. Under poor ecological conditions, they can follow from certain green algae. Greenalgae(Ch/orophyceae)

It is generally considered that their appearance in small, sparse clumps is a good sign (especially in alkaline water) that may indicate that the aquarium is well-equipped. However, if they proliferate they create two main types of problem:

- green filamentous algae; this is probably one of the types of overgrowth most often seen. These algae are very thin and, although they sometimes only grow to a few centimeters in length, they can extend to several dozen centimeters. They reproduce through fragmentation, with one very short filament, invisible to the naked eye, sufficient to colonize an aquarium in a fairly short space of time, if the conditions are right;

- green water; this is caused by the widespread growth of microscopic algae, generally unicellular, which can move around with the help of a flagellum. In a natural setting, these constitute phytoplankton. They often proliferate rapidly when the concentration of nutritional elements (mineral salts), particularly nitrogen, is too high, in strong light.

Blue algae (Cyanophyceae)

Also microscopic, these are extremely ancient in origin: they were among the first living elements to appear on Earth. Despite their name, they form a green-blue, sometimes brownish, layer with a velvety sheen. They often develop if the lighting is excessive.

A disposable razor is useful for eliminatingalgae that grow on the aguariumpanes.

are very sensitive. Any submerged equipment colonized by algae (heating, pipes, diffuser, filter) can be treated in the same way. It is important to rinse and dry them thoroughly before putting them back into the tank. Sometimes, however, the proliferation of algae can be so extensive that the only option is to create a whole new aquarium from scratch.

Ecological methods

Try to regulate the factor provoking the algae overgrowth by adjusting the amount of light, which should be reduced in the case of green or blue algae. Changing the position of the tubes, or the addition of deflectors, to keep algae off the front of the tank, produces good results. In freshwater aquariums, you can make partial water changes, on a fairly regular basis, using water with a low hardness containing few mineral salts.


Be careful, however, not to make any drastic alterations to the quality of the water if this has been specially adjusted to specific plants and fishes. In seawater tanks, change the water, replacing it with reconstituted water of the same salinity.

Biological methods

These can involve the use of herbivorous animals only interested in certain types of algae, such as the fish mentioned above or gastropods (rare in sea water). The battle on the biological front is sometimes fought without any intervention on the part of the aquarist, as larger aquatic plants release substances that can inhibit the development of algae. The extent of this phenomenon is very difficult to appreciate in an aquarium, as it is invisible to the human eye.

Chemical methods

There are special products on the market designed to kill algae. As their effect has not been fully established, it is best to be cautious with the dosage, as these substances probably also affect other plants. For the same reasons, the use of copper sulfate is not recommended, as it is dangerous for invertebrates. There is no miracle solution. The use of several techniques at the same time sometimes has positive results, but it is not unusual to find that the algae reappear after a while. It is best to get used to partially eliminating them on a regular basis.

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