Not recommended, but I had a cherub angel in a 30g reef for over 7 years. The only other fish in the tank were an ocelaris clown and flame hawk. My corals were never picked on. I was never sure what the angel eventually died of. He and the serpent star used to make a show at each other occassionally, but no harm came of it. I still have the other 2 fish and the star. The 30g was definitely at maximum bioload with those 3 fish, but held a very good equilibrium.