Aquarium salt is Sodium Chloride and Epsom salt is Magnesium sulfate
I use both for different treatments/reasons
Espom salt I like to use for constipation, bloat, edema, swim bladder problems for its laxative properties and reduce inflammation/edema,
Aquarium salt I use for healing of wounds parasites/pathogens/fungus/mold etc...
Both have properties for antibacterial/fungal issues to a degree
On both I use a 1tsp/gal to 3tsp/gal for no longer than 10 days and I like to always do treatment in QT so I can do 100% water changes and have my salts pre-mixed so not to over dose.
I try to stay as natural as I can with treatments as I have found the fish tolerates it better
Also, epsom salt is plant safe, aquarium salt can kill some plants especially when used long term