i wouldnt add salt aros are now brackish water fish 
i never add salt for anything
melafix all the way
i dont think it is lack or ox that done it as the was fresh water running into the tank the whole time this problem happened
temp drop would not have caused it
the only thing i can think that made the eye go like that is chlorine burn
melafix is great stuff i use it all the time with my rays with no problems
the only way it chould have been lack of ox is if your tank is badly over stocked
i never add salt for anything
melafix all the way
i dont think it is lack or ox that done it as the was fresh water running into the tank the whole time this problem happened
temp drop would not have caused it
the only thing i can think that made the eye go like that is chlorine burn
melafix is great stuff i use it all the time with my rays with no problems
the only way it chould have been lack of ox is if your tank is badly over stocked