emperor tetra

What’s with this fish? He’s been like this for a week and he got better so we didn’t think much until today, where all of a sudden he’s much worse. I’ve been trying to feed him but he’s not eating at all. I suspect worms so I dosed the tank with 1 tbsp of aquarium salt per 5 gals. Any advice?

Hi, I've had some emperor tetras for 5+ months now and a few months ago 2 got sick, they had severe buyoncy issues, one had a crooked spine and an infected injury as well (the other didn't). I did daily water changes and put medicine in the water suggested at my local fish shop and luckily none...