Firefish issue

[Beano1169]

I figured plus he did come from a tank where there was two of them so its possible he had the injury before hand . I just wanna makre sure it doesnt continue to desintigrate

[Beano1169]

Ok so his fin looks like it has gotten small but not as broken/torn looking. and his face seems to have developed some sort of scrap. Almost looks like a small fuzzy cotton ball, I assume its a fungus of some sort, or since he is white in the face possibly he just scrapped his mouth, he can still "yawn" or open his mouth wide, he is still active and eats. (just fed him a large chunk of mysis) does anyone know what it could possibly be? and if its what I suspect what will treat fungus without killing corals and inverts. I will attempt to put up a picture if possible, he is kinda camera shy. Thanks for the help