This is probably stupid, but is Aquarium salt the same as Epsom salt? Also, where do you get epsom salt? I can only seem to find stuff for people with additives like mint, calamine, etc.
This is a good question!
Aquarium salt is sodium chloride. It is the same as table salt, but it has no anti-caking agents that table salt includes (which are harmful to fish!). It can be added to most tanks as a preventative for external parasites, or at a full dose as part of a treatment for external parasites. It does not replicate brackish environments or create saltwater. Most plants are killed by salt, especially if it's in there for more than a week, and there are several species of fish that cannot tolerate salt and that should be kept in mind when treating the tank for anything.
Epsom salt is magnesium sulfate. It is used as a laxative and helps reduce fluid retention in both humans and fish! It is almost only ever used as a bath, but can occasionally be added directly to the tank.
I got epsom salt at the dollar store! I'm sure most pharmacies sell it.