I have had a yellow regal angel for about a month. From the first day, he was a terrific eater. The menu for the tank includes mysis, angelfish diet, plankton, nori, and clams on the half shell. Suddenly, three days ago, he stopped eating. He swims normally. There is no harassment. He has no spots or heavy breathing, just won't eat. All of the other fish, butterflies and wrasses, are all acting normal. Last night, I did a water change, hoping that may stimulate him. This is a FOWLR tank that has been set up for two years. I have another tank with macro, sponges and gorgs that I could put him. Any suggestions?