help guys.. i bought a purple tang about two weeks ago. the tang has been very happy and nothing has appeared to be wrong with him until recently. the only thing i can think that may have influenced his condition is a water change. after doing a water change a few days ago the tang has seemed to loose color gradually every day since and there appears to be bubble on his body all the time. im not sure if they are bubbles but that is what they look like. can anyone tell me what is going on? what maybe wrong with him and how to fix it? your help would be very much appreciated