Have you tried using Tetra anti-parasite food? I used it when I had my Majestic Angel get ick (AFTER quarantine--yes it does happen!!!) He got beat up everyday by my Sohol Tang, stressed him greatly. Managed to easily catch the tang, but the majestic was always hiding from my nets! Didn't want to dismantle my corals, either. Tetra Anti-Parasite food did the trick for me. I do have a UV Sterlizer in my tank, which I'm sure didn't hurt. Fed it for two weeks. Didn't harm any of my corals. Didn't lose any fish. Ick hasn't returned. That was 7 months ago.
It's hard to find, though...some stores here stocked it before it was removed from the market, so I got lucky and stocked up. You can also soak food in it's main ingredient, metronidazol...but I have no idea what concentration to use. LFS guy swears by the stuff for his reef tank, too. He DOESN'T use UV.
BTW, Sohol now kicking my eels around in the moray tank.