sorry to read all that. And from what you are describing, seems to have something quite bad happening in your tank and consistently ... did you think along the line of any chemical you might be non intentionally adding into your tank ? something like cleaning your tools or bucket used to change the water with soap ... Also you do not seem to have any nice stuff built onto your life rock. Still surprised reading your story that the fish seems OK. If I was you I'd then have a systematic approach to find out what is the problem: for example would use my quarantine tank with a hardy coral with minimum equipment on it and then add one by one items you are using on your main tank (chiller, sump ,,,) and see what will turn my coral dead. My 2 cents but defintively fell sorry for you ...