Calculators / Pool

Is my pool water balanced?

Put in your test readings. You get the Langelier Saturation Index, whether the water is corrosive or scale-forming, and which reading to fix.

Updated November 2026 · How we check our numbers

Balanced

LSI 0.00

Within CDC's −0.3 to +0.3. Keep each reading in its own range too.

LSI: 0.00target −0.3 to +0.3
Temperature factor: 0.70
Calcium factor: 2.00
Alkalinity factor: 2.00

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Estimate for planning only, not professional advice. Check the manufacturer’s instructions, your local code and a licensed professional before you buy, build or install. Use at your own risk. Terms.

LSI = pH 7.4 + TF 0.70 + CF 2.00 + AF 2.00 − 12.1 = 0.00

Each reading

CDC Model Aquatic Health Code

pH7.4; keep 7.2 to 7.6
OK
In range.
Total alkalinity100 ppm; 60 to 180
OK
In range.
Calcium hardness250 ppm; 200 to 400 for plaster
OK
In range.
Cyanuric acid (stabilizer)40 ppm; 90 or less
OK
Fine.

Reading the LSI

Below −0.3 the water is corrosive: it etches plaster and eats metal heaters and ladders. Above +0.3 it's scale-forming: cloudy water and crusty tile lines. CDC's target is −0.3 to +0.3.

What to fix first

Get alkalinity into range first, then pH, then calcium. Retest after each change, with the pump running.

Stabilizer

CDC notes the LSI drops as stabilizer rises but gives no correction, so we haven't applied one. With a lot of stabilizer, aim for the upper half of the range.

How we work it out

LSI = pH + temperature factor + calcium factor + alkalinity factor − 12.1 (12.2 above 1,000 ppm TDS)

Formula, factor table and target (−0.3 to +0.3) are from the CDC's Model Aquatic Health Code, 5th edition. We interpolate between the table's rows. The code also sets pH 7.0 to 7.8 (adjust to 7.2 to 7.6), total alkalinity 60 to 180 ppm, calcium hardness 200 to 400 ppm for plaster and 80 to 200 for vinyl or fiberglass, and stabilizer at 90 ppm or less. It's written for public pools, but it's the clearest public standard there is.

Where the numbers come from

Pool care

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