Hello. I have a question. My tank was running fine and all the fish were happy. I came home from work, fed the fish, and they all ate and seemed fine. The next day my yellow tang was not swimming around like usual. A few hours later he was being devoured by the hermit crabs. The water levels were fine, and so were all the other fish. His body looked all sucked in, and I noticed some brown specks that had fomed on his body near the cadual fin. What the heck happened, and what can I do to prevent this from reoccurring? Incidentally, I had the tang for about 2 months already.