If I'm using RO water and brewing a dark beer (porter), I'm not sure if I should add only enough calcium carbonate to in the mash to treat the mash (4 gallons) or since calcium carbonate only dissolves in the mash, if I need to add enough to the mash to treat the whole 8 gallon preboil. I fear adding too much to the mash will have negative effects on my mash/ph. Help?