Well there are a few different types of salt water tanks. Reef tanks have corals, inverts, fish, and macro algaes. A fish only tank would normally tend to house more aggressive fish that could potentially eat corals/inverts, so these are usually kept with fish and no corals. Then you have all those in between.
How many lbs of live rock would you say you have in there? Also how long has the tank been up? Have you tested your ammonia, nitrite, and nitrates? Also what do you have for filtration?