don't add melafix...it generally isn't a great idea with gars and won't help a ton in this case anyway. add salt if you like, but the fish should be fine. the pbass are probably the culprits, another case for the support of NOT keeping gars with pbass. gars are generally not advisable with rays either.
if you don't want a completely blind gar, i would separate it. good luck--
--solomon