Well, for starters you really shouldnt add that many fish to any tank at once, that is pretty big jump for the bacteria to handle and you might cause a mini cycle. But i would qt him just like the clowns. Although, you run the risk of stressing him more because he is in the qt with the clowns and making your ich issues worse. I personally would return the flame, and wait until after you have put your clowns in the tank to get another one, and then qt that one.
But here is some info on how to treat ich:
Oh No! I have ich! What do I do?
Also, please remember your stocking limit on your tank. Overstocking a tank is an awesome way to stress fish out so they get ich.