sudden xenia decline

[dsaundry]

Heater might be a possibility, is it near any other aggressive corals?? It may have been stung. Don't know if it is savable or not, I had a leather that got stung once{at least that is what I concluded] as all my water parameters were fine. I am assuming all your other corals are showing no signs of stress??
Sometimes corals will just not adapt to a transfer from one tank to another although you said it was growing well so I am less inclined to assume that is the case in this instance. If it really started to go south after your heater failed I think you have to assume that may have been the dagger that killed it..if there is any good frags portions left..