I don't know what you've been reading but magnesium sulphate stimulates the activity of "good guys" or probiotic bacteria.
The calcium present in he usual yogurt carrier for probiotic works against and reduces the amount of magnesium in the body. Most people on a modern Western diet are deficient in magnesium.
The good bacteria feed on the fibrous material of raw vegetation in the diet. If you make the alterations to your diet before commencing the Liver Flushes problem are minimised and you will not have to keen spending out commercial supplements