Lionfish looking Dull and Foggy

[JaiWiz]

I got a small volitan lionfish and he has recently stopped eating and his colours are horrible very dull and foggy i have also noticed his eyes have a little tiny thin layer of fog over them i'am very concerned i'am getting a 70 gallon for him soon and am wondering what is the best natural medicine on the shelf i can give him or any supplements to help him out he is alone in a 30 gallon as we speak. Any suggestions ????