Hi Torbin:
Yes, for bloated fish, you can combine use of *epsom salt (magnesium sulfate) with a metro treatment. Use 1 or 2 teaspoons of epsom salt per 10 gallons.
I don't know why the white feces was expelled right after treatment. I know my healthy fish will poop right after a water change. I think it's all the activity in the tank.
Carol
* epsom salt is different than table salt or aquarium salt