Calcium carbonate will RAISE your mash pH...the CO3- ion has more influence on the mash pH than the Calcium does...the net result is to increase your pH. Besides, it makes things taste chalky.
I generally use equal amounts of CaCl and CaSO4, and some MgSO4 when needed to boost Mg for yeast health in 70+ beers....or to boost SO4 without adding Calcium for Hoppy beers.
I use 88% Lactic to fine-tune pH of the mash and sparge. Generally a ml or 2 is enough for each. You don't want to use more than 3 ml in a 5-6 gallon batch, unless you want the flavor. 3 ml / 5 gallons is the start of the taste threshold. I'm not that sensitive to it, so I can't taste it until about 4.5 ml.
When I make a beer below 10 SRM, I use 50% carbon filtered tap water, 50% Distilled. Then I add 5 grams CaSO4, 10 grams CaCl, and 5 grams MgSO4, and 1.5 ml Lactic....for 4 gallons of Mash water.
I acidify my sparge water to a pH of 5.6 or so.
My resulting profile is:
Calcium Magnesium Sodium Chloride Sulfate Chloride / Sulfate
(Ca ppm) (Mg ppm) (Na ppm) (Cl ppm) (SO4 ppm) Ratio
123 14 12 141 154 0.91
