what myka said its really good, just a little tip, dont freak out everytime one of your corals closes up when you turn your back from the tank, mine do all the time, if you watch it long enough its because of hermits or shrimp or even one fish of mine, they reopen, just recently my leather didnt open for 2 days everything else was fine, and then it just opened( polyps came out) i didnt do anything to that tank or even a water change, i have no idea still what happened.ive got a 20H see here for a pic.
http://www.canreef.com/vbulletin/showthread.php?t=42603