calcs.homes
calcs.homes
The Langelier Saturation Index tells you whether your water will corrode metal and plaster, or scale them with mineral deposits. Enter your four readings for a full water-balance check.
Estimate only — assumes typical (non-saltwater) TDS. Salt pools run slightly scaling by comparison.
LSI equals pH plus a temperature factor, a calcium hardness factor, and an alkalinity factor, minus the constant 12.1. Each factor comes from a standard lookup table — interpolated between listed values — that converts a raw water-temperature, calcium, or alkalinity reading into its corresponding saturation contribution before the four terms are summed.
LSI is the pool industry's standard measure of whether water will dissolve or deposit calcium carbonate. A result between −0.3 and +0.3 is considered balanced; below that range water turns corrosive and etches plaster and pits metal, above it water turns scale-forming and clouds with mineral deposits — both damage equipment and surfaces over time if left uncorrected.
Between −0.3 and +0.3 is considered balanced. Closer to 0.0 is ideal — it means water is neither pulling minerals out of your plaster and equipment nor depositing scale onto them.
Adjust whichever input is furthest from typical range — raising pH, alkalinity, or calcium hardness pushes LSI up (toward scaling); lowering any of them pushes it down (toward corrosive). Change one variable at a time and retest.