I've been reading up on water chemistry and I think
I understand it.
Ideally, I would buy a $75 pH meter. Mash in and then adjust by adding acid to lower or Chalk or baking soda to increase. This would make all my confusion go away.
Since I don't have a pH meter, the next step was to get a water report from Ward Labs and then try the various spreadsheets. EZ Water Calculator v2 seems pretty smart, taking into account the difference between crystal and roasted grain, not just relying on SRM.
Here is my water:
Ca 58, Mg 35, Na 12, Cl 25, SO4 24, Alkalinity as CaCO3 224.
When I enter my water into this for a dark beer with 2lbs roasted and 2lbs crystal, it recommends adding say 6.6g NaHCO3 and 7.2g CaCO3 to hit 5.2 in my 10 gallon mash. This includes a 30% dilution in order to lower my magnesium. This puts my Alkalinity up to 359 and my Residual Alkalinity at 260 and estimates my Mash pH at 5.21.
When I read the sticky "A Brewing Water Chemistry Primer" it says to dilute until your water is soft, which would be 85% for me. Then the baseline is to add 6.8g of CaCl2 and to skip the Sauermalz for a dark beer. If I take those recommendations and put them into the EZ Water Calculator with the same grain estimations, it says my Alkalinity will be 34 and my residual alkalinity will be -12 with an estimated Mash pH of 4.97.
If I do nothing but dilute my water by 30% to lower the Magnesium under 30ppm, then EZ Water says my Alkalinity will be 157 and Residual Alkalinity will be 113 with an estimated Mash pH of 5.08. This seems half-way between the two suggestions. I'm tempted to go this route.
This all leaves me a little confused.
I've read in other threads of people making dark beer with really low alkalinity and their mash pH turns out fine, but the huge disparity between the two methods seems weird, I just don't understand why this can be.
Sorry for the mechanical nature of this post. I know you all probably get tired of offering water profile advice. Is the moral to this story, "go buy a pH meter" ?