Watch the units. Kolbach's /3.5 and /7 divide the hardness, which
is Ca and Mg expressed as CaCO₃ (or as mEq/L). They don't divide the
elemental ppm printed on a water report. Plugging elemental ppm in directly
(Alk − Ca_ppm/3.5 − Mg_ppm/7) understates the mineral offset by 2.5× and
is a common transcription error. In elemental ppm the same formula is:
RA= Alkalinity − Ca_ppm /1.4 − Mg_ppm /1.7
because 2.497 / 3.5 = 1 / 1.402 and 4.118 / 7 = 1 / 1.700. The expression
below is equivalent to both, and the tests check it against the published RA
of Dublin (≈175) and Pilsen (≈6).
Residual alkalinity (Kolbach 1953), ppm as CaCO₃.
Watch the units. Kolbach's
/3.5and/7divide the hardness, which is Ca and Mg expressed as CaCO₃ (or as mEq/L). They don't divide the elemental ppm printed on a water report. Plugging elemental ppm in directly (Alk − Ca_ppm/3.5 − Mg_ppm/7) understates the mineral offset by 2.5× and is a common transcription error. In elemental ppm the same formula is:because
2.497 / 3.5 = 1 / 1.402and4.118 / 7 = 1 / 1.700. The expression below is equivalent to both, and the tests check it against the published RA of Dublin (≈175) and Pilsen (≈6).