Puckorius Scaling Index Calculator
High calcium with low alkalinity can look scale-forming on paper yet deposit almost nothing — the Puckorius index corrects for buffering capacity. Enter four routine values for a scaling-versus-corrosion read.
Puckorius Scaling Index
| Item | Value |
|---|
How the calculation works
Formulas
pHs = (9.3 + A + B) − (C + D) (Langelier saturation pH; A, B, C, D as in the Langelier equation)
pHeq = 1.465 × log10(alkalinity as CaCO3) + 4.54 (equilibrium pH from buffering capacity)
PSI = 2 × pHs − pHeq
pHs = (9.3 + A + B) − (C + D) (Langelier saturation pH; A, B, C, D as in the Langelier equation)
pHeq = 1.465 × log10(alkalinity as CaCO3) + 4.54 (equilibrium pH from buffering capacity)
PSI = 2 × pHs − pHeq
| PSI value | Tendency |
|---|---|
| < 6.0 | Scaling likely |
| 6.0 – 7.0 | Transitional — little scaling or corrosion |
| > 7.0 | Corrosion likely |
Notes & limitations
Puckorius & Brooke (1991), via Puckorius & Cartwright. Unlike the Ryznar index it uses an equilibrium pH derived from alkalinity instead of the measured pH, so it reflects the water’s buffering capacity.
- PSI below 6 predicts calcium carbonate scaling; above 7 it predicts the water will dissolve scale rather than deposit a protective film.
- Because it ignores the measured pH, PSI can disagree with the Langelier and Ryznar indices on low-buffered waters — that disagreement is the point: run both and compare.
- Same input rules as the Langelier family: calcium and alkalinity as CaCO3, TDS as mg/L.
- A screening index only. Confirm scaling or corrosion risk with field observations before chemical feed changes.
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