I would certainly just try to treat it. Here is a thread by Humblefish: https://www.reef2reef.com/threads/popeye.305090/I found out the store is open today. I need some opinions. Would it be better to return it? Does lfs usually care for sick fish? If so, it is better off in their hands.
It's only in one eye, but it should give you an idea for treatment. I stand corrected about the flukes; I didn't know eye flukes existed. But you say there was nothing in the dip, so I doubt it now. I would treat with epsom salt and antibiotics if you're ABSOLUTELY sure there was nothing in the dip.