Sorry I took so long to post...gave you time to post twice before I got mine out.
The other fish have definitely been
exposed, but not necessarily
infected. Just like with people, we are around disease all the time, but we don't always get sick. When a fish's immune system is compromised from stress, poor water quality, deficient diet, etc., they become more susceptible to disease. This is not to say that a healthy fish will never get sick, but it greatly reduces the risk.
I would treat the fish in a separate tank. If the treatment works, you know what to use on the other fish if they do become infected. That's my opinion...take it for what it's worth.
