Among aquarists, Caulerpa is the best known marine macroalgae. There are 75 species of this green algae which come from a variety of geographical areas and environments. The general structure of a Caulerpa inlcudes a runner (the stolen), with roots (rhizoids) and a leaf structure (fronds). The type and shape of the leaves is dependent on the substrate and other environmental conditions. Caulerpa are beneficial in several ways. They provide food for other tank inhabitants by offering a favorable environment for microfauna to develop. The microfauna are eaten by fish and other tank inhabitants. Some fish eat the Caulerpa itself.
Caulerpa have become popular for use in "algae-scrubbing filters" to remove excess ammonia, nitrates, and phosphates from the aquarium. In addition, it helps remove heavy metals and neutralize toxins. Caulerpa also provide a pH buffer and produce chemicals which protect the skin, intestines, and gills of fish.
Caulerpa generally require 9 to 10 hours of light from fluorescent tubes, daily. Their photosynthesis produces oxygen and will also increase the pH. Growing it in a separate container with its light on through the evening when the aquarium light is off will minimize pH fluctuations. In a tank, the specimen will need to be regularly pruned so it does not overtake the tank.
Because some species of Caulerpa, such as Caulerpa taxifolia have invaded coastal waters and are a threat to local environments, the importation of Caulerpa has been limited to only specific genus and species. Once it is introduced into new habitats, it multiplies at a rate of three inches per day and blankets the entire bottom, smothering organisms natural to the ecosystem.