It's not popeye from what I can see, more than likely a simple abbrasion. The water changes your currently doing will not be the cause but increasing the frequencey of water changes for the short term (3-4 over the next week) will be part of the solution.
When a fish suffers a mild injury, it can for the most part heal on it's own. The two most important factors being water quality and diet. If these two components are being met properly (in a relatively stress free environment), the use of meds is almost always not a necessity. Even if your numbers (NH3
) are low/undetectable does not mean the water is free from DOC
/organics, merely the biofilter is functioning correctly and being processed. The opportunistic bacteria will still be able to feed off this available nutrient and make a moutain out of a mole hill so to speak. Increasing water changes over the short term ensures a reduction in these nutrients that would otherwise fuel these bacteria preventing them from getting a foothold. With a properly functioning immune system, the fish can do the rest.