Calcium Sulphate (Gypsum) is an important mineral for its effect on mash and wort pH. Used to harden water when brewing ales and bitters. Use as required depending on water hardness. Gypsum (Calcium Sulphate) adds permanent hardness (calcium ions) to brewing water. 

Calcium levels in the 100 mg/l range are highly desirable, and additives should be considered if your water profile has calcium levels below 50 mg/l. The range 50mg/l to 150 mg/l is preferred for brewing.