I have a 55 gal fish only tank. One flame angel, one purple tang, one percula clown, one banggai cardinal, one fiji devil, one cleaner shrimp, one snail, and about half a dozen hermit crabs. The water tests are perfect: specific gravity 1.023, ph 7.3, ammonia 0, nitrite 0, nitrate 5. The water temp did jump to about 81 for a day. I now have it back down to 78. One of my guests from Thanksgiving I think. The only other change is that we added the purple tang about two weeks before the flame angel started getting sick. But they get along fine. We never see them or any other fish fighting. The flame angel has not eaten for 3 days now. He keeps rubbing himself on rocks and other stuff in the tank. He presents himself to the cleaner shrimp a lot more than usual for cleaning. The flame angle appears to have discoloration of his tail. His blues are not as bright either. The very back part of his tail appears to be missing as if some fighting did go on. That's all the info I have. Any sggestions would be great. I was considering a fresh water dip, but I don't know how or for how long. At any rate, thought I would see what you folks think.