My tang seems to be doing OK, but his bottom fim has a notch of discoloration. At first I thought someone took a hunk out of it but then I looked closer and all it is the fin has turned pale. He eats OK and my water is fine. I have a 75gal w/LR and LS. He has 4 other tank mates, a Coral Beauty, 2 clown fish and a yellowtail tang. The tank is well over a year established and I have well over 50lbs of rock and 170lbs of LS.