I never really like to treat fish unless it is necessary. Clowns typically handle Cuppramine very well, so it's not as big of an issue with this fish.
That being said, I had the same ich issue as you did. I had to remove all the fish, leave the tank fallow, etc, etc. Because of this I want to take every precaution to ensure the health of that tank. I have been leaving fish in
QT for up to 6 weeks just to be sure.
tripper