Plecos are often purchased as living aquarium scrub brushes. A customer sees algae, brings home a small sucker-mouthed catfish, and expects it to clean the tank while surviving on whatever it finds. That plan overlooks one important detail: a pleco is an animal, not maintenance equipment. Different pleco species vary considerably in adult size, diet, behavior, and water requirements. Choosing the right one begins with learning exactly which pleco is being sold.