Dat swollen eye

Did a search and to me it seams that it would simply be the result of a fight between the other dats, 5 from 6-12" in 300g, but I havent seen this kind of swelling before on here. Usually just cloudiness. I told her to do small changes every other day for a while to see if that helps.

Anyways what do you think? This is the only photo I have because I am not at the house and my wife had to take it, wont be back for a while either so whatever help you guys can give would be great.

eats off and on, never a great eater but have had him for at least 6 -9 months now

if its an infection is there something better than salt to add? also I cant set up a quarantine at the moment and it would have to be ray safe