I need a fish that eats only algae (not plants, not fish) and can not be picked on by my monsters, but is not in the least aggressive. It needs to readily eat hair algae, red algae, slime algae, cyanobacteria, etc. It is ok if it eats detritus as well, but the main course needs to be algae. How big the mature size is needs to stay under 2 feet. I know that some plecos eventually stop eating algae, this specimen can't do that. Hair algae is the main thing that needs to be eaten. It needs to be a common fish.