Saturation index calculator

Langelier index from pH, temperature, calcium and alkalinity: is the water scaling or corrosive? Free, no sign-up, and it works on your phone at the pool.

How the math works

LSI = pH + temperature factor + calcium factor + alkalinity factor − TDS factor. Alkalinity is corrected for CYA first: about one third of the CYA reading is subtracted. Aim for −0.3 to +0.3. Below that the water tends to eat plaster and metal. Above it, the water tends to scale.

See the saturation index guide and calcium hardness and scale.