Pool Chemical Dosing Calculator
Works out chlorine, pH and alkalinity doses from the pool volume and your test readings. The chlorine dose is exact; the pH dose is an estimate to be added in stages, because alkalinity changes how the water responds.
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The formula
available chlorine (g) = volume (m³) × ppm rise product (g) = available chlorine ÷ product strength TA rise: ≈ 17 g sodium bicarbonate per m³ per 10 ppm
One part per million is one gram per cubic metre, so the chlorine arithmetic is exact once you know the product strength. The pH figures are approximate by nature — how far the pH moves per gram of acid depends on the alkalinity buffering it, which is why alkalinity is adjusted first and acid is added in halves.
What to watch out for
The order matters more than the amounts:
- Alkalinity — it buffers the pH, so set it first (80–120 ppm) or the pH will not stay where you put it.
- pH — 7.2–7.6. At 8.0 chlorine is only about a quarter as effective as at 7.2, so a high-pH pool can test fine for chlorine and still go green.
- Chlorine — 1–3 ppm free chlorine for normal use.
Safety is not a footnote here. Chlorine and acid together release chlorine gas; granular chlorine products mixed with each other can ignite. One product at a time, into the water, pump running, and store them apart.
Stabiliser (cyanuric acid) is not covered: it builds up with dichlor and trichlor use and is only reduced by replacing water. If free chlorine will not hold, test for it.
Frequently Asked Questions
How much chlorine do I add to my pool?
One gram of available chlorine per cubic metre raises free chlorine by 1 ppm. To take a 45 m³ pool from 1 to 3 ppm with 12.5% liquid chlorine: 45 × 2 = 90 g of chlorine, ÷ 0.125 = 720 g of product, which is about 600 ml.
How do I lower pool pH?
Dry acid (sodium bisulphate) or muriatic acid, added in halves with the pump running and a test in between. Roughly 10 g of dry acid per cubic metre lowers pH by 0.1 at an alkalinity of 100 ppm, but the response depends on alkalinity, so never add the full calculated dose at once.
How much does shocking a pool take?
Shock means raising free chlorine to 10 ppm or more — for a 45 m³ pool at 1 ppm, about 3.2 kg of 12.5% liquid chlorine. Add it at dusk, run the pump overnight, and keep swimmers out until it drops below 5 ppm.