That temp should be fine, Epsom salt and aquarium salt do two different things, yes, if he is struggling I would lower the water level for his comfort.
If the swelling does not go down in 3 days-it does not mean parasite per se', I agree with not medicating unless you have to, I don't use any OTC meds due to their harshness myself, watch his poop, stringy discolored (not the color of their food)
Look at him from above and see if the swelling looks the same on both sides to rule out tumor (not cancer) one side will look bigger or mis-shaped than the other.
Sometimes as a fry they can be fallers or have deformed swim bladder and the symptoms can show up when stressed or if they get too cold or breath in too cold, dry air. Sometimes it will resolve on its own and other times it will not and all you can do is keep them comfy.
Lets hope it is just constipation or a mild cold or swim bladder infection....