Ich Back Again

What kind of tank are running? is it FO or FOWLR or reef? If you have a seperate tank available the best best would be to put the fish in hyposalinity and leave the main tank fish free for atleast 5 weeks. Here is a good read on hypo, http://www.petsforum.com/personal/trevor-jones/hyposalinity.html

Keeping the tank fallow (no fish) for 8 weeks is best, while you hypo all your fish in a seperate tank. No way around this... Doing it myself. To prevent having to do this again, QT all new fish, for at least a month.
Treating SW "Ich"

I agree with pufferpunk. We have tried many, many, methods over the years to try and fight the Marine demon. Eventually it became apparent to us all that the only sure-fire way of beating it was to remove the livestock, and leave the effected system "Fallow" for several months at least (longer, if your patients allow you to).
As for the removed livestock, I suggest that you treat them in a quarantine tank with a good Marine itch medication, with all carbon removed from the filters, and skimmer OFF! Furthermore, I have found that medications are more effective if left in contact with livestock longer, ie, if the instructions say 7 days exposure, leave it for 21 days.

a hyposalinity treatment would less stressful than a FW bath, just put them into QT filled mostly with water from the display and do your frequent WC with water of a much lower salinity until you gradually lower the salinity of the QT to apporiate levels.