This happened once after I moved the tank 30 miles about 8 months ago. My brother gave me his reef tank he didn't know much about it and neither did I when I picked the tank up. He has 2 tangs in a 54g corner, they didn't fight until about the first month when I got the tank. I noticed that the yellow tang looked pale and weak. The brown tang was picking on him pretty bad. After a week of this I though he was gonna die. But he came through and lived. Now its happening again. Is there anything that causes this? The tang is starting to look white again. I know the tang is better then what it was when I got it. I can't get pics right now but has this happened to anyone before?