just started up my 55 gal saltwater tank. i have been planning on a fish only tank for a while now with the intention to start a reef awhile down the road (year or so). I do not particularly want to purchase 300 dollars worth of live rock for the tank right now but what else can i put in the tank to give the fish a place to live. I am gonna start with a couple clowns and then grow from there. what kind of other rocks or decoration can i use?