I wouldn't do just an Epsom salt bath.... I would leave him in the Epsom salt solution.
Since you said the popeye is severe to the point where you're concerned about the eye coming out, I would follow OFL's Epsom salt treatment plan. It starts out with a dosage of approx 1 teaspoon Epsom salt per gal on the first day, then brings it up to 3 teaspoons per gallon over the course of several days. The entire treatment can be done for 10-14 days.
OFL's Epsom salt treatment:
- Add 3 teaspoons Epsom salt to one gal of conditioned water.
- Stir/shake until the Epsom salt is completely dissolved.
- Using this premixed treatment water, make 25% water changes every 15 min for 1 hour today.
- Tomorrow, do a 50% water change using this premixed treatment water.
- Then, every other day for 10-14 days, do a 50% water change using this premixed treatment water.