The true algae eaters are a single-genus family (Gyrinocheilidae, Gyrinocheilus) of small Southeast Asian fish that live in fast-flowing water, hold on to fixed objects using a sucker-like mouth, and feed primarily on algae.
The Chinese Algae Eater (Gyrinocheilus aymonieri) is sometimes kept in aquaria to control algae. It can range up to 28 cm in length, but aquarium residents tend to be under 10 cm. It has a reputation for becoming increasingly jealous of its territory as it matures.
Two other Gyrinocheilus species, rarely seen in the aquarium trade, are the Spotted Algae Eater (Gyrinocheilus pennocki) and the Borneo Algae Eater (Gyrinocheilus pustulosus).
The Siamese Algae Eater (Crossocheilus siamensis) is a more gregarious and tolerant Cyprinid that ranges up to 15 cm. It is the only fish that will also graze on 'Black Brush Algae,' which are freshwater Rhodophyta, or Red algae.
American-Flag Fish (Jordaniella floridae) are also dependable algae eating fish. Many Loricariid catfish of South America constantly graze algae and biofilm.
(mention other species also called algae eaters)