my devils hand turned black and melted overnite - my long tentacled plate which is 2 weeks old has developed a pie shaped dead spot and my brain coral is showing its skeleton in places - water parameters are perfect - have them on the bottom of the tank under 2 400w MH - have a couple of tangs/ crabs and an urchin -plus assorted snails - i give up - what is going on - corals seem to die on me constantly.