Here are two scenarios about PH and RA for your imput.
This is a water report, soft water:
Total hardness CaCO3=24
Alkalinity as CaCO3=20
note. calculation from EZ water calculator 2.0:
1)Brew a recipe for a ligh ale with about 10lb grist, no crystal nor roasted malts, SRM=3, mash water =3.8gals
Starting mash PH is high(5.6). Adding 3g of CaCl2 and 2g of epsom salt and 2g of lactic acid will make my mash PH =5.36/ RA would be -200.
Why adding this instead of just lactic acid? To build some minimum Ca, Cl/SO4 ratio, getting PH down as a plus.
What about -200, is that ok, although much lower than the range suggested by Palmer (-60 to 0)?
2)Brew a recipe for a stout with 13.8lb grist, 2lb crystal and 3/4lb roasted, SRM=36, mash water=5gals
Starting PH is low (4.90). SO4 and Cl are almost nothing as well as Chloride. Gotta pick something to add that rise PH right, baking soda or chalk?
If adding baking soda only, would need 10g
If adding chalk only, would need 30g
I assume this much chalk would make my beer taste like drywall
A combination of both, like 8g baking soda and and 2g chalk would bring my PH up to 5.20 (good).
My Ca would also rise to 50.
At this point, sulfate is still nothing, do I care? probably not right, otherwise I wold have to add somehitng that woud lower my PH again.
Finally, the RA after the 8g of baking soda and 2g of chalk would be 287. Good?
Edit: For the stout, before Ajdelange hit me with a hammer :-) , should one with a good PH meter check the mash PH first, then decide if adding chalk or bicarbonate is necessary to increase PH?