Since you have it in a QT
already I would use Maracyn II at double the dose daily for 7 days total. Fungus problems are usually not what they appear and commonly gram negative bacteria. Be sure it is not Lympho either (warty instead of cottony). There is no treament for that.
, had you left the fish in the main the other fish would not normally have been at risk. This can typically be fixed without any treatment. Increasing the frequency of water changes, boosting the foods nutrition and reducing stress will allow the fish's immune system to do the job.