Gypsum (1 lb) (WM10LB)

Calcium Sulfate. Used to add permanent hardness (Calcium ions) to brewing water. 1 gram in 1 gallon changes the salt levels by 61.5 ppm calcium, 147.5 ppm sulfate and adds 153.5 ppm to the hardness.

Promash is a useful utility to calculate water salts.