Mastering Pool Water Balance with LSI

Why the Langelier Saturation Index is the ultimate metric for pool health.

Water is a hungry solvent. If it doesn't have enough minerals, it will 'eat' them from your pool's plaster or heat exchanger. If it has too many, it will dump them as ugly scale. The Langelier Saturation Index (LSI) is the mathematical formula used to determine if your water is corrosive, scaling, or perfectly balanced.

To calculate LSI, you need six measurements: pH, total alkalinity, calcium hardness, cyanuric acid (CYA), water temperature, and total dissolved solids (TDS). Each of these factors contributes to whether calcium carbonate stays in solution or precipitates out.

An LSI score of 0.0 is perfect balance. A score below -0.3 is considered corrosive (aggressive), while a score above +0.3 indicates scaling water. Maintaining your pool within the -0.3 to +0.3 range is the best way to protect your equipment and ensure swimmer comfort.

FAQ

Does temperature affect LSI?

Yes, significantly. As water gets warmer, it becomes more scaling. This is why you may see scale in your heater even if the pool water seems balanced.