Total carbonate C_T (mmol/L) implied by an alkalinity and a pH.
From Alk = C_T·(α₁ + 2α₂):
C_T= Alk /f_carbonic(pH)
The strict definition of alkalinity also includes + [OH⁻] − [H⁺]. We drop
those terms. Across the pH 6–8.5 range of brewing water they never exceed
3 × 10⁻⁴ mEq/L, three to four orders of magnitude below any real alkalinity.
Keeping them would give a water reported as "alkalinity 0 at pH 7.5" (which
is what RO water is) a non-zero carbonate content, and a mash pH slightly off
its grist's DI pH. We'd rather zero alkalinity give exactly zero.
Total carbonate
C_T(mmol/L) implied by an alkalinity and a pH.From
Alk = C_T·(α₁ + 2α₂):The strict definition of alkalinity also includes
+ [OH⁻] − [H⁺]. We drop those terms. Across the pH 6–8.5 range of brewing water they never exceed 3 × 10⁻⁴ mEq/L, three to four orders of magnitude below any real alkalinity. Keeping them would give a water reported as "alkalinity 0 at pH 7.5" (which is what RO water is) a non-zero carbonate content, and a mash pH slightly off its grist's DI pH. We'd rather zero alkalinity give exactly zero.