It is important to remember that ICK can also be a stress induced sickness the fish can aquire. Like a human, when a fish is stressed out the immune system takes a beating. Which in turn makes the fish more prone to ICK. So it is important to let the fish get established, and take its time doing this. From your previous post you said that your tang seeked out your cleaner shrimps, then this is a good sign, the tang is beginning to acclimate to his surroundings. IMO I feel that having a separate tank to quaranteen a fish in after he is already been in your main tank, will cause unneeded stess to the fish, and prolong the ICK accurance.
With my first blue tang every time he came down with ICK I would fresh water dip him. The ICK would go away temporarily, but would flair up after a couple of days. I did this several times with the same response from the fish. Then I said the hell with it and left him alone, it cleared up with in a week. So this is one case where I found that less is more.
Give the cleaner shrimp time to work their magic, and like Josh said try the garlic food. ;)
IMO some fish take longer than others to acclimate. Some do it in a few weeks. Others it might take months, but once a fish has fully acclimated they become very hardy, and resistant to their owners foolish mistakes.