I have had a sail fin tang for about a month and a half or so in my 90g. I feed him flake food and a large amount of nori every 2 -3 days he usually eats it all within an hour or so. Today I went to feed him and I noticed that the back edge of his Dorsal fin has small holes in it right on the edge of the fin as if someone poked through it with a needle many times I can't get pics cause he won't hold still. If this is fin rot I want to stop it as soon as possible. I put some nori in because I hadn't put it in in 3 days and I thought maybe he just was missing his nutrients, but he hasn't seemed to notice it. All I have in the tank is 2 clowns, 1 coral beauty angel, 1 peppermint shrimp, and the sail fin. I have noticed no aggression between any fish and the tang and the angel I bought out of a tank that they had been living in together for months with no aggression. He has good color, and doesn't seem to act any different. Pls help