I played around with Palmer’s spreadsheet & came up with this. I am no expert by any means but using Palmer’s spreadsheet has dramatically improved my beer. I really recommend downloading the spreadsheet! I’m confident someone else will have more precise input but here ya go… Cheers!!!
For 7 gallons of your water for the mash resulting in a RA ~54 for a ~10 SRM beer leaning towards the bitter side:
Gypsum CaSO4 2H2O = 1 gram
Calcium Chloride CaCl22H2O = 2 grams
Epsom Salt MgSO4 *7H2O = 2 grams
Baking Soda NaHCO3 = 1 gram
88% Lactic Acid = 1ml
Adjusted Mash:
Calcium (ppm) = 74
Magnesium (ppm) =9
Alkalinity as CaCO3 = 134
Sodium (ppm) = 11
Chloride (ppm) = 37
Sulfate (ppm) = 68