Jim,
Ich has to be introduced into a system for fish to get it. Ich is an extremely opportunistic parasite and does not hang around a tank waiting for a fish to have a lowered immune system to become active. If there is ich in a tank, you can be sure it will attach to your fish and begin its life cycle. As long as there are fish in a tank that are not being successfully treated for ich, the ich will continue their life cycle indefinitely until either the fish are dead or the fish have been removed for 6 weeks during which time the ich have no hosts and will die.
Any new additions to any of your tanks lately? Using tools on an infected tank with other tanks can spread ich. Check all tanks for ich, especially if there have been new additions, including macroalgae, corals, sand from someone's tank - just anything new at all over the past month or so.
I have ich in my 72 gal because I did not quarantine one fish that had one spot of ich on its dorsal fin (did not notice this until it was already in the reef). Am currently cycling a 20g hospital tank to treat the fish with hyposalinity:
http://www.petsforum.com/personal/tr...osalinity.html
Have used Kick Ick with no success. Am now soaking the PE mysis normally fed to the fish in the 72g with copious amounts of Garlic Xtreme and Zoe, though I have always used one drop of GE and lots of Zoe all the time I have had these fish. I don't expect the garlic to solve my ich problem, but it is something to try while the hospital tank finishes cycling. I may get lucky with the GE, which would save a lot of trouble so I wouldn't have to break down my reef to remove the affected fish.
As of this moment, my fish are not infected as far as I can see, which means the little monsters are in the sandbed in their cysts waiting to hatch and infect my fish to an even greater extent than they have previously.
Cycle, hospital tank, CYCLE!!!!