In a QT tank, you can give it a try. I've heard some good reports about RxP, but some people also have reported no efficacy. In a QT tank, it won't hurt to try, but I think hyposalinity is a better possibility.
Ich's life cycle is about 14 days at 78 degrees F. To be safe, I'd wait a month. Elevating the temperature slightly (say, to 82 degrees F) is a good idea to help speed metabolism/life cycle.