Thank you so much for your help and advice!
I changed 50% of the water last night and another 50% again today. I'll probably do another water change again tomorrow to help get rid of the salt. I've switched him back to pellet food and the tank temp is now 78 degrees.
The light that came with the tank broke a long time ago so he has only been getting what natural light came in the tank. I bought him a new light today and have it on a timer. How long do you recommend it should be on for?
He doesn't seem to notice the bubbler at all I keep it at a very low setting so there is very little water movement. He has a cave to hide in and a tall plant to swim in, though he likes to hang out behind the heater…
Thank you again! Hopefully we can get him back to being happy soon!