mike dunagan gave you the link on the first page of this post- but here is what dr joe said about NOT using aquarium salt, ONLY epson for bloat/dropsy.
EPSOM SALT may help reduce the internal pressure caused by the swelling. Extremely good aeration is necessary here due to the use of such high temperatures.
NEVER USE SALT (sodium chloride, a.k.a. aquarium salt) for treatment of dropsy. This will KILL your fish in a very short time. The affected fish are already having a difficult time getting rid of salts due to kidney dysfunction. This causes the blown up appearance and concurrent scale standing. The osmotic imbalance caused by addition of sodium to your tank water will make this condition far worse.
EPSOM SALT on the other hand, does not pass through the walls of the gut or gills and will extract water OUT of the surrounding tissue into the gut where it *may* be excreted.
the link (which is a great one!) is on the first page-look there and its on mike d's reply to you..