Popeye can be the result of bacterial problems or aggressive behavior where the fish gets injured. In most cases, improving the water quality and feeding with vitamin fortified foods (Selcon or Zoecon) will help clear it up. Doing a few large water changes with well aged SW
over the next week should help improve the water quality and introduce magnesium which will aid in helping the problem. In milder cases, meds are not usually needed.
I would not suggest moving the fish to a QT
at this point unless the fish is being harrased by tank mates. Moving/netting the fish can often make the eye problem worse causing the fish to lose the eye. Having the QT
set up and ready wuld be a good idea just in case though.