Since he's already in your display, just try to make sure he stays well fed...you can try Garlic or Selcon soaked foods...(not sure if they really help or not, but worth a shot).
Otherwise you can take the more extreme, but proper route and pull all your fish in QT and let the tank run fallow while you treat with copper or hypo.
Otherwise you can take the more extreme, but proper route and pull all your fish in QT and let the tank run fallow while you treat with copper or hypo.

