Well, sadly, the damage is done... The only real cure for ich in your tank is prevention. But I want to stress that QT without treatment is not good enough. I did that once, and still ended up with ich in my DT, even though the fish did not show any symptoms while in the QT. But they obviously were still carriers.
However, when I have used this method, I have been 100% successful. And as described, there are many other benefits, too, with getting your new fish strong and healthy before going into your DT.
http://www.advancedaquarist.com/2007/6/fish
http://www.reefsanctuary.com/forums/...t-process.html