LSI Formula: LSI = pH - pHs pHs = (9.3 + A + B) - (C + D) where: A = (Log10[TDS] - 1)/10 = 0.15 B = -13.12 x Log10(oC + 273) + 34.55 = 2.09 at 25 °C and 1.09 at 82 °C C = Log10[Ca2+ as CaCO3] - 0.4 = 1.78 (Ca2+ as CaCO3 is also called Calcium Hardness and is calculated as=2.5(Ca2+)) D = Log10[alkalinity as CaCO3] = 1.53