My blue tang has responded well to Stop Parasites made by Chem-Marin. I increased the temp from 78 to ~81* to speed up the ich life cycle and haven't kept the lights on as much - (but this is driving my anemone crazy b/c now he's moving all over the place). My clowns and damsels don't seem to have any indications of ich, and I plan to continue treatment for 2 weeks. But if you do this treatment, make sure to monitor you pH daily, it will most likely drop, and you'll have to have some buffer on hand to add to the tank. I plan on getting a cleaner shrimp, more snails and crabs, and a algae blenny. Although I'd like to fix the ich problem before adding them, I don't want to fix it, only to have an outbreak possibly happen all over again when I add the rest to the tank later. Good Luck w/ your purple tang and keep posting updates on what you're doing.