Scaling indices — Langelier (LSI) and Ryznar (RSI)
Calculate the Langelier Saturation Index and Ryznar Stability Index from pH, temperature, TDS, calcium hardness and alkalinity, with interpretation for scaling or corrosive tendency.
Results
| Saturation pH (pHs) | 7,93 |
|---|---|
| Langelier Saturation Index (LSI) | -0,43 |
| Ryznar Stability Index (RSI) | 8,36 |
LSI -0,43: approximately balanced water — close to calcium carbonate saturation at these conditions. RSI 8,36 reads undersaturated while the LSI does not — the two are different empirical fits and can disagree near the boundaries. Treat the water as borderline.
Formula used
LSI = pH − pHs
RSI = 2 × pHs − pH
pHs = (9.3 + A + B) − (C + D)
A = (log10(TDS) − 1) ÷ 10
B = −13.12 × log10(T + 273) + 34.55
C = log10(Ca) − 0.4
D = log10(Alk)
- pH
- measured pH of the water
- pHs
- pH of calcium carbonate saturation
- TDS
- total dissolved solids, mg/L
- T
- water temperature, °C
- Ca
- calcium hardness, mg/L as CaCO3
- Alk
- total alkalinity, mg/L as CaCO3
Carrier method approximation of the Langelier Saturation Index; Ryznar Stability Index per Ryznar (1944). Indicative for waters roughly 0–80 °C and TDS below 10 000 mg/L. LSI above +0.5 suggests scaling, below −0.5 corrosive tendency; RSI below 6 scaling, above 7 corrosive. Lab report lists bicarbonate instead of alkalinity? Alkalinity as CaCO3 ≈ HCO3 (mg/L) × 0.82 — and calcium as the ion: Ca hardness as CaCO3 = Ca (mg/L) × 2.5.
Equipment for this duty
Send the water analysis and duty point, and the branch confirms exact selections, pricing and lead times — usually within one working day.
Request a quoteResults are indicative engineering estimates based on standard formulas and typical assumptions. They are not a design service; confirm any design against a full water analysis and the relevant manufacturer’s data.