Free tool
Pool LSI calculator
The Langelier Saturation Index tells you whether water will dissolve surfaces (corrosive), deposit scale, or leave them alone. Enter your readings and get the index with a factor breakdown. Everything runs in your browser.
-0.02
Balanced
Within the generally accepted -0.3 to +0.3 range. Keep readings steady.
Factor breakdown
pH: 7.50 · Temperature factor: 0.67 · Calcium factor: 2.00 · Alkalinity factor (CYA-corrected): 1.90 · TDS constant: -12.10
Calculated with the standard industry method: LSI = pH + temperature factor + calcium factor + alkalinity factor (corrected for cyanurate: TA − CYA/3) − TDS constant (12.1 up to 1,000 ppm TDS, 12.2 above). Estimates for guidance; balance decisions on plaster, heaters, and salt cells should also follow the equipment manufacturer's requirements.
Why LSI matters more than any single reading
A pool can have textbook chlorine and still be eating its plaster, because balance is a property of the combination: pH, temperature, calcium, alkalinity, and dissolved solids together decide whether water is hungry for calcium or oversaturated with it. That is what the index compresses into one number. Corrosive water (below −0.3) etches plaster and pits heat exchangers; scale-forming water (above +0.3) clouds, stains tile lines, and coats salt cells. Both cost your customers real money, and both can happen with "good" chlorine numbers.
Once you know the index, the fix is ordinary dosing: our chemical dosage calculator covers the amounts, and our guide to billing for chemicals covers who pays for them.
Track readings per pool, visit after visit.
In PoolBase, techs log chemistry at the pool with in-range checks, and every customer gets a service report automatically. Free for 14 days.