I think there is a chain of events. Having grown enormous colonies of colt coral, I have learned that they are a canary in the mine. Mine grew like a weed for months, then in a period of 48 hours melted into ammonia and other foul smelling substances. Everything else was fine, until the colt melted. I would cut the coral back to a chewing gum sized stub on it's rock and sure enough in 6 months it was almost back again. Then it happened again..and again...and now it's on it 4th cycle. Any salinity spike seems to kill it...and it goes from visible daily growth to dead in a matter of 48 hours. There seems to be no pulling it out of on of these dives. They do shrink every now and then, but when they melt they turn really toxic fast. Could easily kill the fish. Xenia can act the same way, grows like weeds...until it doesn't. It at least isn't as foul as the colt coral is when it dies.