Sorry for digging up this thread. I got a similar problem now, and my purple dottyback, which is the only fish in the tank has been getting ich on and off daily. Sometimes the duration would delay for a day or so, then the white spots would come again.
I've tried using real garlic, chopped them up into small pieces, soaked them in warm water with frozen mysis shrimp and then feed it to the fish. There would be some improvement initially, but the white spot would resurface again. Will using real garlic be the same compared to the commercial type of garlic sold in LFS? Please advise.