Is the only visible condition still the eye? Scrutinize the fish, check everything including the gills. Have you rechecked the water parameters? How old/large is this guy?
Another possibility would be parasites(possibly internal), cataracts, bacteria or another problem, but I would suspect cataracts only if the fish is older but the new behavior wouldnt be explained by this. Parasites or bacteria would probably also infect your other fish. Has this guy always been a good eater, or does he get out-competed alot and only eats a little?
If it isnt your water parameters, the cloudy eyes could be a symptom of a more serious problem that you are not seeing. Without really knowing what is going on, salt and water changes might not be doing anything. Im not familiar with dats, so posting in the datnoid section might help you if they are predisposed to any sort of illness or condition. Hope he starts doing better, GL