It'd be great if you posted a picture..
ok since the QT is 8 gallons id put the infected fish back in the main tank and keep the other fish in the QT because he will be able to cope with the unfiltered water better. you might not need meds, just perfect water and salt it might clear up by itself, and even if you do need meds you will just have to cycle the tank again, you cant just let your fish die because you cant be bothered to help him.