Tetras' fascinating schooling behavior and vibrant colors make them frequent aquarium residents. However, most tetras are small and cannot deal with brutal tank mates. This means you need to select algae eaters with care, since some species with a reputation for algae-eating may harm small, delicate fish like tetras. You have a number of different options from several families of fish.
Suckermouth Catfish (Plecos)
The suckermouth catfish or plecos come from the same general area as many common tetras: the Amazon drainage in South America. You have to pick plecos carefully, since not all species work in tetra aquariums. Otto cats (Otocinclus spp.) make great tank mates for tetras. Ottos stay under 2 inches and live in groups, similar to most tetras. The clown peckoltia (Peckoltia vittata) gets to be a bit larger at 4 inches and can live singly; it generally will not harm tetras. The bristlenose plecos (Ancistrus spp.) vary in size, since this genus includes several species. However, most max out at 4 inches and the largest reach only 6 inches. They also do not harm tetras, though they may fight among themselves, so keep only one bristlenose per tank.
Carp Family Algae Eaters
A number of fish from the minnow/carp family make good algae eaters. The flying fox (Epalzeorhynchos kalopterus) will nibble on algae. Additionally, the Siamese algae eater (Crossocheilus siamensis) will eat brush algae—which many algae eaters ignore. However, the Siamese algae eater closely resembles other species, some of which make poor algae eaters and may pick on tetras. To determine if you have a real Siamese algae eater, look at the stripe on the side of the tail. On true Siamese algae eaters, you will see a solid black stripe that runs from the tip of the nose through the eye and straight through the center of the tail. If the stripe stops at the base of the tail or you see more than one line, you have something else.
Hillstream Loaches: A Definite Maybe
Hillstream loaches, sometimes sold as Borneo plecos or butterfly plecos—common names can be tricky—also make great algae eaters. These fish resemble tiny stingrays and rasp algae off surfaces like real plecos. However, they may not make the best tank mates for tetras. Hillstream loaches need strong currents and slightly colder water than most tetras. Still, research your exact species of tetra, since some species do like strong current and conditions that are slightly less than tropical.
If you're not married to the idea of an algae eater with a backbone, some freshwater invertebrates make decent algae eaters. The Amano shrimp (Caridina multidentata) resembles the more common ghost shrimp (Palaemonetes spp.), which also eats algae. However, Amano shrimp will eat brush algae. Snails can also make good algae eaters, but some species can harm plants and overrun an aquarium in the wrong conditions. These small invertebrates will not harm tetras, and most tetras will not harm them either.
Algae Eaters to Watch Out For
Pet shops often sell "algae eaters" that are lousy at the job. This includes a few plecos and the Chinese algae eater or CAE (Gyrinocheilus aymonieri). The common pleco (Hypostomus plecostomus) will certainly eat algae. However, it can also grow to about 2 feet within a few years. Pet shops and zoos rarely take them, leaving you stuck with a giant fish that needs a huge aquarium. Additionally, a few species of pleco called panaques (Panaque spp.) get very territorial and may harm tetras. Unlike plecos, the CAE doesn't eat much algae as it grows, preferring fish food. They also grow to about 10 inches and will attack other fish, including tetras.