Crossocheilus siamensis, or Siamese Algae Eater (seen here in the bottom of the image) eats red algae; i.e., the unsightly brush algae that can ruin a planted tank. It is the only fish known to do so.  This fish is from Thailand and the Malaya peninsula.  It is very good natured, and well suited for a community tank.  The SAE is often confused with other types of algae eating fish.  When purchasing this fish, be sure that the long stripe along its body continues through the tail fin, and that the fins are clear otherwise.  See Algae Eating Cyprinids for further details on how to distinguish this fish from other types of "algae eaters".  SAEs can retail cheaply in the United States (under $1.50) when carried by a local fish store.  It may be hard to find at a local retailer however, in which case ordering on-line may be the only way to obtain these wonderful workhorses of the planted tank.  Ordering on-line is typically more expensive.  I have seen prices as high as $6.00 US for an  SAE at an on-line retailer.  Because of its red algae eating penchant, its benevolent disposition and interesting schooling behavior, a group of these fish is almost an essential addition to a high-light, high-growth planted tank.