Why LSI matters for your pool.
A clear pool can still be out of calcium carbonate balance. LSI gives us a more complete picture than pH alone.
← Back to Water ChemistryWhat does the Langelier Saturation Index measure?
The Langelier Saturation Index (LSI) estimates whether water is likely to dissolve or deposit calcium carbonate. A strongly negative LSI can indicate calcium-carbonate dissolution potential, especially relevant to cement-based finishes. A strongly positive LSI can increase calcium-scale potential.
Why we look at several readings together
Temperature, pH, calcium hardness, alkalinity adjusted for cyanuric acid, and dissolved solids all influence the calculation. The same pH can produce a different LSI in summer and winter.
Our preferred approach
Pure Pools generally targets 80–100 ppm alkalinity and 350–400 ppm calcium hardness where appropriate for the pool, then adjusts pH with the overall LSI in mind. These are company preferences, not universal requirements. Finish type, manufacturer guidance and applicable regulations come first.
Does an appropriate LSI guarantee equipment protection?
No. LSI describes calcium carbonate saturation, not all forms of corrosion, metal damage or sanitizer performance. Proper filtration, disinfection and compatible equipment remain essential.
For additional reading, see Orenda's LSI education article.
Continue learning about water chemistry.
Explore more of the science behind Pure Pools' approach or review your pool's readings in our calculator.