I don't do Epsoms at all because I only have 50% of my kidneys. Some practitioners say not to use it, it's too hard on the kidneys and gives false results because it can mix with the oil and create stones immediately, so you're not really getting out old stones.
Instead, take herbs/malic acid/phosfood to crush the stones up and build up the liver's strength so it really gushes out the bile and pushes those pesky little stones out.