Magnesium Sulphate Heptahydrate (MgSO4·7H2O) as the heptahydrate sulfate mineral epsomite of Magnesium Sulphate, commonly called Epsom salt. In gardening and other agriculture, magnesium sulphate is used to correct a magnesium or sulfur deficiency in soil; magnesium is an essential element in the chlorophyll molecule, and sulfur is another important micronutrient. It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, roses, tomatoes, lemon trees, carrots, and peppers. The advantage of magnesium sulphate over other magnesium soil amendments (such as dolomitic lime) is its high solubility, which also allows the option of foliar feeding. Solutions of magnesium sulphate are also nearly neutral, as compared to alkaline salts of magnesium, as found in limestone; therefore, the use of magnesium sulphate as a magnesium source for soil does not significantly change the soil pH value.
Magnesium sulphate heptahydrate is also used to maintain the magnesium concentration in marine aquaria which contain large amounts of stony corals, as it is slowly depleted in their calcification process. In a magnesium-deficient marine aquarium, calcium and alkalinity concentrations are very difficult to control because not enough magnesium is present to stabilize these ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate.