Epsom salt (Magnesium Sulfate) is good for symptom of edema/swelling type problems that can be seen with bloat, popeye, dropsy...it will also work as a laxative...it has a antibacterial/fungal effects as well
Short term use is recommend, however, I have used it long term in low doses for aquarium plant food without any issue.
Good starting dose for swelling, bloat, constipation, popeye, dropsy symptoms is 1tsp/gal up to 3tsp/gal-with popeye and dropsy I increase to 2tsp/gal on day 3 of a 10 day treatment and 3tsp/gal with pineconning
If 2-3tsp/gal used it is best to also do a slow decrease of salt once the treatment is completed to 1tsp/gal for a full 24 hours before placing back in freshwater
Making 100% daily water changes along with the Epsom salt is also important for full effect of the treatment in general.
Adding tannins can also be helpful by using Indian almond leaf or Oak leaf
Correct dosage can be made easier if you pre-mix the salt, tannins, dechlorinator in a 1gal jug-this will steep the leaves and dissolve the salts and ease the daily water change routine
Treatment is best when done in QT