^^^^^^^I was typing while HumbleFish was posting, so you're getting about the same info twice^^^^
Real black ich is a worm and Prazi-Pro will usually take care of it. Its the safest med I know of, can even be used in a reef tank. It will kill featherdusters, though. Just to CMA: I know of several folks who have used it in a reef and have talked to a few company tech-types and they all feel comfortable using it in a reef. I've used PP for years in my QT, so never had to worry about using it in my reefs. I honestly don't know if i would or not; so, officially, I consider it safe in other peoples reefs. If you have a FOWLR; then use it in the DT. it will also kill flukes and other parasitic worms; on both the inside and outside of the fish. It should be part of any QT routine, IMO & IME.
Another consideration, black ich is contagious, so all fish need to be treated.