As Leebca wrote above, fish can develop an immunity to ICH given good food, water and a stress free environment.
I chose to remove all of my fish and treat them in a QT. I cycled the hospital tank prior to moving the fish into it. They are currently into their 6th week and are doing fabulous. They have been treated with cupramine and dewormed. In two more weeks they will be placed back into the reef which has remained fallow for the full 8 weeks. The water quality is excellent in the hospital tank and has remained that way during the entire treatment. I attribute that to a carefully, fully cycled tank and weekly large water changes.
To prevent disease in my reef, in the future, I will QT every fish and coral I receive.
