PLEASE HELP. My fish is sick and I don't know how to fix him.

I had thought my fish, Enjy, had fin rot. His fins were looking a bit torn and ragged, his gills looked red, and he was getting lethargic. He's been eating and making a small bubble nest. I recently moved and had to make a water change. I use conditioner and whatnot. I realized I was not cleaning it often enough and that my heater was likely promoting bacterial growth. I decided to treat Enjy for fin rot. I began the treatment after about a week of his lethargy and a few days of noticing a change in his appearance.

Last night I put Enjy in a 1/3 gallon quarantine bowl. I put in fresh water with conditioner and aquarium salt. There's a heater in the bowl to keep him comfortable. Enjy acted like he felt some better today, but he's still lying in the bottom of the bowl a lot. He's just actually moving around when I walk by. I've seen him swim to the top for air, and once some condensation fell in the bowl and he jumped up to "eat." While he's acting better, his body looks worse. His gills look red and are protruding slightly. They look as if they're bloody. I think he may actually have ammonia poisoning. What do I do? Should I change his water and out in the BettaFix medication I got for him? Should I add more salt? Should I leave him be? I'm really concerned about him. Please help! I'm afraid his time may be getting short.
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