Saturation pH (pHs)

Computes the pH at which calcium carbonate is in equilibrium between dissolution and precipitation. Used as the reference pH for LSI, RSI, and PSI.

$${\text{pH}}_s=(9.3+A+B)-(C+D)$$

Variables

Symbol	Meaning	Unit
A	Total dissolved solids term, A = (log10(TDS) - 1) / 10	unitless
B	Temperature term, B = -13.12 x log10(T+273) + 34.55, with T in degrees Celsius	unitless
C	Calcium hardness term, C = log10(Ca hardness as CaCO3) - 0.4	unitless
D	Alkalinity term, D = log10(Total Alkalinity as CaCO3)	unitless

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Part of The Blueprint of Water