Originally Posted by Alienbetta1
Epsom salt is basically the same as Aquarium salt.
Epsom salt and aquarium salt are Not the same thing and have two different actions along with some same actions
If he was in a neglected temporary holding cup at the store, he most likely has several things happening.
Ammonia being the big problem and you took care of that by placing him in clean dechloranted water.
Fin rot-daily 100% water changes with aquarium salt 1tsp/gal for 10 day can help in mild cases, however, in advanced stages you may want to use a broad spectrum antibiotic, I don't use them so I can't advise.
Possible parasite like velvet that can kill the fish if left untreated, I use natural method same as for the fin rot and I turn the lights off.
Be careful with over treatment in an already stressed fish especially with OTC medication.
Keep up with the daily water changes to improve his environment and strengthen his immune response.