Since he's new to your setup, he could have carried flukes in on him. My yellow tang had flukes when I got him, I only noticed it when one eye became cloudy. A couple of rounds of Prazi cleared that up.
Flukes are really difficult to see with the naked eye when they're on your fish. Only was to know for sure is to freshwater dip him and see if you see any translucent sesame seed sized things left behind in the dip bowl. If you can catch him easily you might put him back in QT for a precautionary Prazi treatment.
Otherwise, just keep an eye on him. If worse comes to worst, you can if necessary dose Prazi into your display tank without killing corals/inverts. If he does have flukes, they may spread to your other fish, and I know from experience they can be fatal.