My captive bred yellow tang suddenly died out of nowhere while I'm away today. I found it on the sand bed. All my other fishes are fine. I couldn't figure out why, I had the fish for more than 1 and half year. No new additions recently also. It is also quite plump, dun have any obvious physcial damage as well ick. I can show the photo if need to. Think not good to post in the forum. I do have a another bigger blue hippo tang, he will pick on it once in a while but not super agressive as I dont see any obvious fight marks. Any possible reasons?