murph had a good suggestion. I have a yellow watchman goby with my two clowns. They are good fish for a smaller tank because they only grow to 2", are very non-aggressive and like a lot of liverock to hide in. The yellow watchman is a bright yellow with blue spots on its back. A sand substate is a good idea with any goby, they need a bolthole in the substrate or find holes in rock they feel is safe. Without the security of a hiding spot they will get stressed. They are very fun to watch hover above the sand.