Calcium Sulfate (CaSO4) is a source of Calcium (Ca) an essential component of cell wall structure and plant integrity, as well as transport of other nutrients. Sulfur (S) is essential for root development.
Also used to increase General Hardness (GH)
1/2 tsp into 10 gallons will add 10ppm Calcium
Calcium Sulfate Dihydrate(CaSO4.2H2O) 97%
Information regarding the heavy metal content of this product can be found at Association of American Plant Food Control Officials