I have had a long tentacle plate coral in my 75 gallon for about a month. He was doing fine until last friday when he started dying. He started losing tissue from the middle, and now it is spreading outward. His tentacles don't inflate as much. I keep params roughly what is in my sig. I DID move him two weeks ago to the center of the tank. Before he had been near the rockwork. I had LEDs on at about 60 percent. there is no brown jelly or anything. I did have a cardinal fish that started hosting in him at times 2 weeks ago. I have made sure he is well fed. I have had some sand stir-ups but they've all settled. nitrates are around 5 or so. Any idea what else I can do or what could be killing him?