sick fish
sick fish
If you can get them out that's great, plus any other fish you have in there. And you'll need to set up a quarintine tank 10 -20gal pref , easier to treat ( cost effective too ) . You'll want to treat the ich first, cause that will ( sometimes ) make them stop eating. Sounds like your banner has popeye, which isn't too common with salt but it does happen. I had a squirrel fish with it. Melafix , cured it in a week. Coppersafe will cure the ich, and you'll want to treat seperately . While I don't think there would be a bad mix with the 2 meds I wouldn't want to try it.
Coppersafe works the best for ich, but it's not particular which invertibrate it kills. So not possible in the tank. After 3 weeks with no fish to thrive ( live? ) on the ich in the tank will die. Your parameters didn't cause these problems, most likely you got something new that brought it. Or recently you've gotten something that was hiding in a rock.