Te other day I noticed that my bubble coral, which I have had for about tree weeks, was suddenly not looking so good. It has been closed mostly, no more tentacles at night, and a small brownish tuft has appeared at the tip of one of the skeletal ridges. Oddly enough, all of my other corals are appearing more healthy and open since this has happened. Any I dead as to what might be going on? My water parameters are normal.