Free Online Calculators
Dose pH & chlorine for your pool volume
This calculator works out your pool volume from its shape and dimensions, then the grams of pH-Minus or pH-Plus and 65 % chlorine granules needed to reach your targets, plus a shock dose of 15 g per m³. It uses 150 g pH-Minus or 100 g pH-Plus per 0.1 pH and 10 m³, and 1.5 g of granules per m³ and mg/l. Product labels take precedence.
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Start with your pool's water volume in gallons, then compare each measured reading (pH, free chlorine, total alkalinity, calcium hardness, cyanuric acid) against its target range. The dose is the gap between current and target multiplied by the volume and the strength of the product you are using.
There is no single best app — what matters is that the tool lets you enter your exact pool volume, your test results and the specific product strength you own. A web calculator that shows the dose per chemical works just as well as an app, since the underlying math is identical.
Aim for slightly alkaline pH, free chlorine in the recommended sanitizer range, balanced total alkalinity to keep pH stable, calcium hardness suited to your surface, and cyanuric acid high enough to protect chlorine from sunlight without stalling it. Balance them in order: alkalinity first, then pH, then sanitizer.
This calculator doses pH-Minus granules (sodium bisulfate), not muriatic acid, and has no alkalinity field, so use the dosing chart on your acid's label for that. For comparison: 10,000 US gallons are about 37.9 m³, and lowering pH from 7.8 to 7.4 there takes about 2,270 g of pH-Minus in this calculator. Add acid in portions with the pump running, then retest before adding more.
The pH and total alkalinity crash, leaving water that is corrosive to plaster, grout, metal fittings, heaters and pump seals, and irritating to skin and eyes. You then have to raise pH and alkalinity back up with soda ash or sodium bicarbonate.
It scales with the volume and with how far pH and alkalinity sit above their targets, so the same pool needs very different amounts depending on the test results. Calculate the dose from your readings rather than using a fixed amount per pool size.
Only if the calculated dose for your volume and readings actually calls for that much — on a small pool it would drive the pH far too low. Split large doses across several additions with circulation and retesting in between.
Evening or early morning works best, with the pump running, so the acid disperses while nobody is swimming and sunlight is not driving off chlorine at the same time. Avoid dosing right before heavy bather use.
Adjust pH and alkalinity with acid first, then shock once the water has circulated and been retested. Chlorine works far more effectively at a balanced pH, and mixing the two products directly is dangerous.
Clear, safe pool water comes from regular testing and correct dosing. This free pool chemistry calculator works out your water volume from the pool's dimensions and then how much pH-Minus or pH-Plus and how much chlorine granules you need to reach your targets. It also shows a shock treatment amount.
Results are in grams. The calculator assumes fixed products: pH-Minus based on sodium bisulfate, pH-Plus based on sodium carbonate and chlorine granules with 65 % available chlorine. For liquid chlorine, tablets, muriatic acid or other strengths, use the dosing on the product label, which always takes precedence.
If pH is within 0.1 of the target, or chlorine is short by 0.1 mg/l or less, the calculator shows "No adjustment needed".
| Volume | pH-Minus per −0.1 | pH-Plus per +0.1 | Chlorine +0.5 mg/l | Shock |
|---|---|---|---|---|
| 10 m³ | 150 g | 100 g | 8 g | 150 g |
| 20 m³ | 300 g | 200 g | 15 g | 300 g |
| 30 m³ | 450 g | 300 g | 23 g | 450 g |
| 50 m³ | 750 g | 500 g | 38 g | 750 g |
Your pool holds 20,000 litres, so you enter 20 m³ manually. After a sunny weekend you measure pH 7.9 and 0.5 ppm chlorine and want pH 7.4 and 1.5 ppm. The calculator shows 1,500 g of pH-Minus (five steps of 0.1 × 150 g × 2) and 30 g of 65 % chlorine granules; the shock amount is 300 g. Split large pH doses into several additions and retest in between.
pH controls how well chlorine works: at pH 7.2 about two thirds of free chlorine is present as strongly disinfecting hypochlorous acid, at 7.5 about half, at 8.0 only about a quarter. That is why the calculator's note says to correct pH first, let the water circulate, retest and then add chlorine, with granules pre-dissolved in a bucket of water. The note also says not to swim above 3 mg/l chlorine; after a shock treatment, wait until the level has dropped below that. The US CDC recommends at least 1 ppm free chlorine in pools and a pH of 7.2–7.8.
Total alkalinity, calcium hardness and cyanuric acid also affect how stable pH and chlorine stay. The calculator does not ask for them; use a full test kit and the product instructions for those values.
Rectangle: length × width × average depth. Round: π × (diameter ÷ 2)² × depth; 5 m across and 1.5 m deep gives 29.5 m³. The calculator treats oval pools as ellipses: π × half length × half width × depth, so 8 × 4 × 1.5 m gives 37.7 m³. For a sloping floor, use the average of the shallow and deep end.
It depends on bather load, sunlight and water temperature. Let your test result decide: when chlorine is below your target, enter current and target values and add the amount shown.
Over-chlorination irritates eyes, skin and airways and can bleach swimwear and liners. Stop adding chlorine and keep the pump running; the calculator's note says not to swim above 3 mg/l.
Yes, it is free and needs no registration.
It is designed for swimming pools. Hot tubs use different target values and often different products, so follow the manufacturer's instructions.