Galaxy Pond Ale

I'm planning to brew the highly rated Galaxy Pond Ale from the Brewsmith website, http://beersmithrecipes.com/viewrecipe/3684/galaxy-pond-pale-ale
the original brewer has added 15.28g of Calcium Sulphate to the mash there are no other mineral additions so I'm wondering if his base was RO water or just his local tapwater. It seems like a lot of Gypsum to add.

Without any information on the water profile for that recipe, I would ignore the mineral additions and add them as you would for your water source and profile desired.