One of the major uses of magnesium sulfate is in agriculture and gardening where it is used as a fertilizer Magnesium sulfate is used in bath salts. Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in marine aquaria Magnesium sulfate is used as the electrolyte to prepare copper sulfate Magnesium sulfate is used as a brewing salt in production to adjust the ion content of the brewing water It is used in paper making industry Magnesium Sulphate Heptahydrate is also used as laboratory reagent.