I do not see where it is going to alleviate popeye.
I sure didn't mean to imply that epsom salts were a cure for popeye or dropsy. It can provide relief from the symptoms. The eyes in popeye swell because of fluid retention.
1/8 teaspoon per every 5 gallons of water is the recommended dosage. This does not take the place of an anti-biotic. As I said in my previous post - a broad spectrum anti-biotic is normally recommened. The mixing of maracyn and maracyn 2 is good way to cover all bases.
Pinkertd - epsom salts work in humans as a laxative because they make it into the intestines. Unless you're going to give your fish an enima, they don't make it to a fishes intestine in any real significant amount. That's why I say it's not a true laxative for a fish. It does draw fluids out of the fish, which in turn reduce the swelling of popeye, dropsy or bloat. It's the reduction in swelling that gives the fish some relief from the symptoms. For bloat, it allows things to move along a bit better and in the case of popeye can help prevent permenent eye or brain damage. (Fish eyes, close to fish brains - swelling is bad.)
As for dropsy fish and the kidney thing - as far as I see it, by the time a fish blows up with dropsy, the kidneys are damaged beyond repair. Any of my fish get it they are euthanized on the spot. But a lot of people like to try to treat them. Epsom salts, if nothing else, provide a little relief from the bloating symptom.
So I guess you could stay that my use of epsom salts with fish is strickly for relief of symptoms. Sort of like you might take asprin for a headache that is the result of the flu. The asprin doesn't do dittly for flu virus at all, but getting rid of the headace sure doesn't hurt ...