best and safest bet are snails, snails, and more snails. Get several different types that do different things (nassarius, trochas, Cerith, Margaritas, astrea, Turbo) about 1 per gallon total. You can go with hermits but the only some what safe choice is Scarlet Reef hermits and even those some people have trouble with. Crabs like Sally Lightfoot or emerald are risky. I personally have had good luck with both but you never know until you buy a crab and put it in your tank if it is going to eat algae/detrius or coral/fish. brittle stars are nice but several people have had trouble with them taking out their fish. I have never had one so I can't say either way.