I'd drop the Cu to as close to .35 if as you can. (use carbon, Cuprisorb, or just Wcs to slowly remove some copper. be careful not to go below about .35, even briefly. When a fish stops eating, that is often the first sign of copper intolerance. Taking several days to go from "0" CU to about .35-.40 usually helps. Tangs seldom have problems with Cupramine, IME. Cu at .35 is completely effective against ich. If the tang isn't breathing heavily, gasping, etc.; I wouldn't worry if he goes several days without eating; but wouldn't be surprised to him feed with a slight drop in Cu. Don't go below .35 though, unless the tang really looks like he's in trouble. BTW, fish can go much longer without eating than is often realized. This will give some folks "the vapors''; but even going two weeks without eating isn't going to hurt most fish. But having a parasite, secondary problems, while not eating is.
Edited duplicate post, sorry.
Edit: I wouldn't add any other meds with the copper