I have one sand sifting starfish..He does a great job in my 20g long..keeps my sandbed so clean..and my lawnmower blenny helps eating the hair algae. and my other crabs and snails do a good job too...I used to have 1 yellow watchman and pistol shrimp.they kept me busy fixing my rock and digging the sand to find my missing corals that been burried under the sand. some of my corals died because of them. YWM died, jumped out the tank. I sold the pistol, now i'm free