The Best Freshwater Algae Eater

Algae-eating fish are helpful in aquariums as they keep the bottom, sides and decor clean. Lots of fish are touted as algae eaters, so choose one based not on appearance but on a species' ability to survive in a tank with fish who have similar tank temperature and size requirements.

  1. Black Mollies

    • Black mollies get along with most freshwater fish. Mollies like to swim with others of their own kind; the best way to group them is to bring together two to three females to every male. If you have a tank smaller than 20 gallons, start with just two fish. The black mollie not only eats algae off the sides of the tank, it skims the water of the surface in search of bits of floating algae. The molly stays small, growing up to 3 inches as an adult.

    Oto Cat

    • The oto cat, also called the dwarf sucker mouth, is gaining in popularity as a good algae eater for community tanks with a big algae problem because they work quickly. They love to move in schools of at least six, if your tank can accommodate such a large school. They don't like to be alone, and will hide and move skittishly about the tank unless they have at least two more of their kind. Having more than one should be easy, since they grow to about 1.5 inches. Be prepared to drop in algae discs once your tank is cleared of algae, as the otos will die if they have no algae left to eat.

    Rosy Barbs

    • Rosy barbs are colorful algae and plant eaters who grow to about 5 inches long. If your tank is 30 gallons or larger, you've got the ideal setup for rosy barbs. They do best when cohabiting in groups of at least five of their own kind; they are highly stressed if forced to live in a community tank with no other rosy barbs. They get along well with other fish and will keep your tank free of algae. They also eat vegetation, so plant only hardy underwater plants or be prepared to replace them often.

    Avoid Plecos

    • Though touted as the best freshwater algae-eating fish, plecos are not nearly as good for your tank as the sales clerks would have you believe. They're found in just about every pet store in the United States and are foisted upon unsuspecting novice fish keepers as the ultimate algae eaters. But plecos grow to 18 to 24 inches, and most people cannot accommodate fish that size. Plecos aren't suitable for a home aquarium, but they do better in small outdoor freshwater ponds.