I have a bubble coral. He has been in the tank for many years and always has done great until recently. For the last couple of weeks he has not open up hardly at all. All of my other Corals are doing great and I see no evidence of anyone bother him. My parameters have not changed and as a pre-caution I just changed/cleaned all of my filters. The only theory I have is something caused him to get stressed and he has not recovered. Any ideas on something to try.