Pool LSI and chemical dosing calculator.
Enter one water test. Get your Langelier Saturation Index and doses to target, in the order you should add them. Same chemistry engine as the LOADLESS app.
Scale-forming — scale and cloudy water risk
Doses to target, in order
- 27 fl oz Muriatic acid 31.45%
pH 7.8 → 7.5. Add half, circulate 30 min, retest. - 9.4 lb Calcium chloride 77%
CH 250 → 300 - 1.2 lb Stabilizer (CYA)
CYA 30 → 40 - 0.25 gal (32 fl oz) Liquid chlorine 12.5%
FC 1 → 3 (add last)
Targets: FC 3 · pH 7.5 · TA 90 · CH 300 · CYA 40 · Salt 3,200. Estimates for typical product strengths. Add in stages, circulate, retest, and follow the label.
Running this on 200 pools a week?
Inside LOADLESS, every test is saved to the pool, scored for algae, scaling and corrosion risk, and the risky ones land on your Daily Brief for the right tech.
How to read your LSI
The Langelier Saturation Index tells you whether water will dissolve things (corrosive) or deposit things (scale). It combines pH, temperature, calcium hardness and carbonate alkalinity into one number.
| LSI | Verdict | What you'll see |
|---|---|---|
| Below −0.3 | Corrosive | Etched plaster, pitted metal, heater damage |
| −0.3 to −0.2 | Slightly corrosive | Slow wear over the season |
| −0.2 to +0.2 | Balanced | Where you want to live |
| +0.2 to +0.3 | Slightly scale-forming | Early scale at the waterline |
| Above +0.3 | Scale-forming | Cloudy water, scale on tile, clogged salt cells |
The formula
LSI = pH + TF + (log₁₀ CH − 0.4) + log₁₀(carbonate alkalinity) − C. TF is the temperature factor (0.6 at 76°F, 0.7 at 84°F, interpolated between). Carbonate alkalinity is TA minus about a third of CYA. C is 12.1, or 12.2 for salt pools at 1,000 ppm or more.
Dose rules of thumb (per 10,000 gallons)
- Liquid chlorine 12.5%: about 10.7 fl oz raises FC 1 ppm.
- Muriatic acid 31.45%: about 50 fl oz × pH drop × (TA ÷ 100).
- Soda ash: about 30 oz by weight × pH rise.
- Baking soda: 1.5 lb raises TA 10 ppm.
- Calcium chloride 77%: 1.25 lb raises CH 10 ppm.
- Stabilizer: 13 oz raises CYA 10 ppm.
- Pool salt: 8.3 lb raises salt 100 ppm.
Common questions
What is a good LSI for a pool?
Between −0.3 and +0.3 is balanced, and closer to 0 is better. Below −0.3 the water is corrosive and can etch plaster and damage metal. Above +0.3 it is scale-forming.
Why does cyanuric acid change the LSI?
Part of total alkalinity is cyanurate, not carbonate. The LSI uses carbonate alkalinity, so this calculator subtracts about one third of your CYA from TA before calculating.
In what order should I add pool chemicals?
Adjust alkalinity first, then pH, then calcium, then stabilizer, and sanitizer last. Add one chemical at a time, circulate, and retest before the next.
How do I lower CYA?
Only by dilution. Partially drain and refill. The calculator estimates how much water to replace when CYA is above 90 ppm.
Why is the constant 12.2 for salt pools?
Salt pools carry high total dissolved solids, which shifts the saturation point. The calculator uses 12.1 normally and 12.2 when salt is 1,000 ppm or more.
Water's balanced. Is the business?
LOADLESS reads every test and everything around it, then tells you only what needs you.