What's going on?!

[YellowFinsReef]

I have a really nice sized kole tang that eats very well. Recently it developed a pop eye on is left face. I'm not sure how that came about. Currently the kole tang shares a 40G quarantine with some other fish I have been quarantining. The parameters are unstable because it's a quarantine system, but I change the water often to meet the needs. The salinity is at 1.020. Thoughts anyone on causes & treatments?

 

[Humblefish]

You can treat with Furan-2 + Kanaplex + Metroplex for an infection.

Also, dose Epsom salt (1 tablespoon per 5 gals) to help ease the swelling.