Langelier Saturation Index (LSI) Calculator
Predict calcium carbonate scaling vs. corrosion tendency from pH, temperature, calcium hardness, alkalinity and TDS — plus the Ryznar Stability Index.
Formulas
LSI = pH − pHs · pHs = (9.3 + A + B) − (C + D)
A = (log₁₀TDS − 1)/10 · B = −13.12·log₁₀(T+273) + 34.55 (T in °C)
C = log₁₀(Ca as CaCO₃) − 0.4 · D = log₁₀(alkalinity as CaCO₃)
RSI = 2·pHs − pH
LSI below −0.5: corrosive · −0.5 to +0.5: balanced · above +0.5: scaling
RSI below 6: scaling · 6–7: neutral · above 7: corrosive
LSI = pH − pHs · pHs = (9.3 + A + B) − (C + D)
A = (log₁₀TDS − 1)/10 · B = −13.12·log₁₀(T+273) + 34.55 (T in °C)
C = log₁₀(Ca as CaCO₃) − 0.4 · D = log₁₀(alkalinity as CaCO₃)
RSI = 2·pHs − pH
LSI below −0.5: corrosive · −0.5 to +0.5: balanced · above +0.5: scaling
RSI below 6: scaling · 6–7: neutral · above 7: corrosive