If the fish is not showing signs of ich, don't treat him for it. This will only create unneeded stress on the fish. Once again, most fish will fight it off on their own if left untreated. Once you use copper in a tank, it is useless for anything else. You will never be able to keep any inverts in there, ever. Take a look at my Tang above. He fought off that level of ich with no treatement at all. There were five other fish in the tank with him and no other fish ever came down with it either. It's been over a year and my tank is still ich free.
Don't panic. Oftentimes ich is brought on by stress, especially in Tangs. A lot of reefers will not even qt their fish because switching tanks brings extra stress to the fish. Oftentimes, a fish won't show sign of ich in a qt by himself, only to get it once in a community tank.
There are many opinions on this subject, but, as long as he is still eating and swimming, I am a firm believer in letting him fight ich off with no meds. I think he'll be a much healthier fish afterwards