Reef clean-up crews are vital for the health of a reef tank.  Algae irritates corals & can kill some by overgrowing the coral.  A natural way to keep algae at bay is our clean-up crew!  Heads up though!  Many sell hermit crabs as part of their clean-up crew package but I will NOT sell them as hermit crabs of any color or size (yes, even tiny ones) can harm corals, at the very least will irritate many with their picking behavior!  Add to that they are true Carnivores (meat eaters!) & are often the culprit for dead snails & fish that jump tanks!  Though you may not "see" them do anything wrong, I assure you they are most active at night when dark & will even nip at sleeping fish which spooks them & they fly out of the tank!  Stick with my clean-up crew critters that cover all areas needed & eliminate the chance of disasters with other cleaners.