At least once a month i go and stop by a boat harbor near by my house, and watch all the fish in it. The fish that are in the harbor are mostly tangs and butterflyfish. Every time i go i see tons of moorish idols pecking at the rocks and feeding on them, and they are really fat. The stuff on the rocks they are eating is just this brown stuff and Its pretty funny that they even eat it. I want to get a moorish idol for my 55 SW, but know how hard it is to get them to eat. So I was wondering if i got some of the rocks from the harbor, and just kept replacing the rocks every few weeks or so, would that be fine for the fish.