So all I have to do is go to the grocery store/wal mart and find any box of Epsom salt?
Yup. Just make sure it only Epsom salt and not with perfumes or whatever. Here in Sweden I had to make a special order to get "clean" epsom salt - the only kinds I could find of the shelves where died and perfumed.
Now I found a supplier so I won't have any problem when my supply runs out in about 10 years