Calcium chloride is usually used in place of Gypsum when sulfates are not desired. 
Calcium chloride will adjust your mash pH down. 
1 gram in 1 gallon changes the salt levels by 72 ppm calcium, 127.5 ppm chloride and adds 180 ppm to the hardness.
https://www.brewersfriend.com/water-chemistry/https://docs.brewfather.app/recipes/water-calculat...