If you have Andreas book he says if you need to you can use magnesium citrate, it comes in a bottle at the drugstore. Epsom Salts does not hurt the kidneys (see link) it is magnesium, not salt.
You could take less ES too and try that. A lot of people don't like the ES and don't use it, I am not one of them.
Julia Chang from sensible health does not use it. Ask MH feels you should use the ES. So you can make your choice.
Johanna
PS: if you know if you have calcified stones for sure I would stick with the ES.