Did you put the epsom salt directly in the water or are you treating the food with it?
One trick I've been told that helped me to cure up some internal parasites on angelfish was to get 1cup of tank water, add 2 tablespoons of epsom salt to the cup, let dissolve, then add your flake or pellet food to the cup. let sit for 10 minutes or so to absorb the salt into the food, and then feed to the fish (disposing of the epsom salt/water). That way you guarantee the fish actually consume the salt for it's stool-softening power.