Rudy,
A FOWLR setup can be very difficult to maintain parasite free when you are dealing with predators such as puffers etc. It is true as Drew stated that Cleaner wrasse do not remove Ich, rather the tissue etc. that is damaged from parasites and other minor injuries on a day to day basis.
If you have "full blown Ich" on these fish in question then we agree in removing them from the system and treating immediately in a lower salinity and higher temperature, maybe 82 degrees. Although live rock is a great biological filter and natural surrounding for the fish, the price you pay is the inability to medicate. In our experience with the feeding demands on predators, and using a FOWLR system, this will not be the last time you experience this. The waste levels are much higher then a typical fish only system, and the aggression between species will increase stress levels.
Are you running a UV sterilizer? If not that would be a must in this type of system. Proper sizing and flow rates are key for a successful kill rate of Ich. Circulation in the aquarium can probably be increased to reduce dead spots as well where the eggs accumulate as does organic waste. Is there a protein skimmer on the system? Hypo-salinity can help as suggested but your best prevention is with a UV and removing the fish and treating in a quarantine tank.
Good luck,
Big Al's BC