They are good scavengers. Haven't heard or seen that they do much for algae control. I believe a pair is better than one. They stay together and set up a "fish wash" in a section of the tank. The fish seem to enjoy the process and it is fun to watch. There is argument as to wether or not they eat the crptocaryon irritans parasite(ich).They do ,however,keep many parasites off the fish. I would not rely on them for ich treatment.