Magnesium sulfate is more commonly known as Epsom salts, and is used to treat brewing water. Magnesium is beneficial as a yeast nutrient in small amounts (10-30 ppm). Sulfates are used in brewing to accentuate hop bitterness and are usually used at a rate of 50-350 ppm. 1 gram per gallon will usually add around 100 ppm of sulfate and around 25 ppm of magnesium to brewing water.