ye get some predatory fish in there. well something of teh sort u know like a hawk. my hawk doesnt bother other non aggresive fish, but kills a lot of pests. i put in live rock the other day and saw the weirdest and scary looking worm and i was a bout to put my hand in and pull it out when my red spotted hawk stuck his hed in a hole of the rock and ripped the worm out. i think he ate it. he also eats those little crawling centipede things that come on live rock. i dont know wat there called.