Lots of times, more established fish have a much stronger immune system than recently introduced fish. however, this is not to say they won't get it. I would get a QT set-up, and get your tang treated, without treating the main tank, before the clowns do get it. If they do, then they may have to move to the QT also. But don't assume the clowns are immune, they may just be able to fight it for longer.
Woo Hoo, PAYDAY! Time to pay the LFS
rent (even before I pay mine
Join the Alabama Regional Forum!