You have a whole mess of things goin on 1) You need to triple your light output(whatever LFS told you that a 2 bulb t5 fixture is good enough for coral doesnt care about their customers or the animals they sell.)2)You should be changing 10 to 15% of your water monthly at least but ideally every 1 to 2 weeks. 3)Power filters are not really meant for Reef Tanks they harbor Nitrates, For fish only they are ok but definitely not if you are serious about coral throw it away and buy a decent skimmer. these 3 things add up to bad news in a Reef Tank. I would suggest doing a little bit of reading and truly find out just what you need to keep corals successfully. There is enough good info on this forum to to tell you all you need to know. I would read the "new" to saltwater thread from top to bottom its excellent reading