Hello everyone,
Its been months since I've posted here but I have been "lurking." I'm sorry for being so inactive

My betta Kokomo who I've had for years now is sick and I'm having trouble coming up with a diagnosis:
I left him in my apartment in his filtered, heated (80 degrees) and planted 5 gallon tank for 5 days for Christmas break. In his tank was one of those "seven day betta feeder" tablets that was almost completely dissolved when I returned. I noticed when I got back that he was having trouble swimming to the surface to eat despite having the same large appetite as always. I moved him into a 1 gallon tank with his heater so that he could surface easier. To this tank I added about 1/4 teaspoon aquarium salt and bettafix. He was also fasted for a week but did not improve. He tries to swim but ends up falling back down and it's almost like he is being weighted down by his tail and has to drag himself around. He is still eating and moving around the small tank as much as he can but I think he's getting worse, I should mention that I see NO bloating at this point.
I'm so sorry for such a long post, thank you so much for any advice you may be able to give me!