Free pool tool
Pool LSI Calculator
Check whether your pool water is corrosive, balanced, or scaling. Enter your test readings below — the Langelier Saturation Index updates instantly. No signup required.
Your water readings
Enter your test results. The index updates as you type.
Langelier Saturation Index
Water chemistry is balanced.
The LSI estimates whether your water is likely to corrode surfaces and equipment (negative) or deposit scale (positive). Aim for −0.3 to +0.3.
What is the Langelier Saturation Index?
The Langelier Saturation Index (LSI) measures whether pool water is in chemical balance. It combines five readings — pH, water temperature, calcium hardness, total alkalinity, and cyanuric acid — into a single number.
- Below −0.3 (corrosive): water can etch plaster and stain or pit metal. It pulls minerals out of surfaces and equipment.
- −0.3 to +0.3 (balanced): the target range — water neither corrodes nor deposits scale.
- Above +0.3 (scaling): calcium deposits build on surfaces and equipment, and water can turn cloudy.
Aim to keep your pool in the balanced range year-round. Because the index depends on temperature, the same water can drift corrosive in winter and scaling in summer — which is why pros check it on every visit.
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