Definition:

Algae is any of a wide variety of photosynthetic organisms lacking a vascular system. They may be unicellular, filamentous, or, in the case of seaweeds, large and complex in form. They may grow on substrates or float in the water. The following may occur in freshwater aquariums: blue-green algae (not true algae, but closely related to bacteria), diatoms (unicellular), red algae (multicellular), and green algae (unicellular or multicellular).


Algae occurs in aquariums where there is too much light, too little light, or too large a supply of nutrients (nitrate, phosphate), that is, dirty water. Reducing the supply of nutrients, adjusting the lighting and putting algae eating fish in the tank, are the best methods for combating algae.