I have a 30 gallon reef tank with about 35 pounds of live rock. I have a clown fish, 6 line wrasse, and a yellow damsel (added in that order). I have a variety of inverts- sea urchin, sand-sifting starfish, pom pom crabs, snails. I'd like to add a fourth fish, but I'm worried about compatibility. Would a royal gramma work with this group? Any suggestions?