new sick fish????

[sea gnome]

Bought a yellow tang 3 days ago. Supposedly been there for 1 month and had been sick, now better. It was thin but ate well while I was there. Now he's in my tank and eating very well but I notice gold spots all over him (marine velvet?) The other fish seem fine, no one is flashing but the tang's fins have two spots where they are sliced. I have no hospital tank, no comments please. I have been feeding garlic to them and everyone is indulging. Any thoughts? Rachel