Just keep up with the epsom salt and water changes and he should make it through.
The epsom is to help flush any chemicals out, and the water changes are to help with that and the cloudy eyes.
Don't worry about his fins falling off a little bit. That happened to my boy, he lost about half his finnage from the rays to the webbing, but it grew back pretty quick. Just offer a high protein diet like you would be if you wanted to spawn him anyway, so no real changes there and just keep the water a bit cleaner than normal.
As far as heater function, definitely should be sealed, so there shouldn't be any moisture or condensation on the inside of the glass. I recommend getting an Eheim Jager (Very good brand, a bit big and a little pricey, but they're adjustable and reliable).
This is my guy after two days of twice daily water changes and epsom salt at 2 tsp/gal: