Pool Dosing Calculator
How much liquid chlorine and acid will your pool use in summer and in winter, and what size dosing pump does it need? This free pool chlorine calculator works it out from three answers: the pool’s volume, how warm the water gets at the peak of summer, and how many swimmers it has on a hot, busy day. Made for aquatic centres, councils, schools, pool builders and service technicians across Australia.
Questions about pool dosing
How much liquid chlorine does a pool use a day?
It depends on three things: swimmers, sunlight and water temperature. Each swimmer uses 4 to 8 g of chlorine. Strong sun destroys most of the chlorine in an outdoor pool without stabiliser within a day, and warm water uses chlorine faster. A busy 1 million litre outdoor pool at 28 to 32 °C, with 1,500 swimmers, can use about 105 litres of 12.5% liquid chlorine a day with stabiliser, and about 160 litres without.
What size dosing pump does my pool need?
Size the pump for the worst case: the busiest hour of a hot, busy day, without stabiliser. Then choose a pump that delivers that at no more than 70% of its capacity, so it never runs flat out. For the 1 million litre pool above, the liquid chlorine pump needs at least 42 L/h.
Should an outdoor pool use stabiliser?
Stabiliser (cyanuric acid) shields chlorine from the sun, so an outdoor pool with stabiliser uses far less chlorine. Most outdoor pools in Australia use it, but the amount in the water is often unknown, so the calculator shows the chlorine both with and without it. Indoor pools are out of the sun and do not need it.
32% or 15% acid?
Pool acid (hydrochloric acid) is usually sold at 32%. A weaker 15% acid is also available. It takes about 2.3 times the litres, and a dosing pump about 2.3 times the size, so the calculator shows both.
How accurate is the calculator?
It is an estimate to plan with, built from published research and pool codes, with 20% added on top to be on the safe side. The sources are listed under “How we calculated this”. Every pool is different: test the water and adjust, and call us on 1300 585 820 to check a dosing pump for your site.
How can the dosing be automated?
A CHEMTROL® pool controller measures the chlorine and pH and runs the dosing pumps for you, and you can see and control it from your computer, tablet or phone. Build yours in the Model Configurator, or find a pump in the Dosing Pump Selector.
How we calculated this
Liquid chlorine
A pool loses chlorine three ways, and we add them up for the day:
- Swimmers. Each swimmer uses 4 to 8 g of chlorine, as measured in recent studies. The litres to buy take the middle, 6 g, with 20% added on top to be on the safe side; the pump sizes take the top, 8 g.
- Sunlight, outdoors only. Without stabiliser, strong sun destroys about a third of the chlorine every hour, up to 90% in a day; with stabiliser the loss drops to about 15% a day. This is why we show both.
- Warm water. Chlorine breaks down faster as water warms, about twice as fast for every 5.6 °C. We use the top of the temperature range you chose.
The litres are of 12.5% liquid chlorine (sodium hypochlorite), which holds about 125 g of chlorine in a litre.
Acid
Most of a pool's acid (over 90%) is not used against the chlorine. It replaces the carbon dioxide the water gives off to the air, which pushes the pH up. So acid follows the pool's size, its warmth and how much the water is stirred by swimmers, not the chlorine. The chlorine itself adds a little, as liquid chlorine carries some caustic soda.
The litres are shown for 32% hydrochloric acid, the usual pool acid, and for a weaker 15% acid. A litre of 32% acid holds about 370 g of hydrochloric acid and a litre of 15% about 160 g, so 15% acid takes about 2.3 times the litres, and a pump 2.3 times the size. As with the chlorine, the litres to buy have 20% added on top to be on the safe side.
The dosing pump size
A pool's busiest hour needs about twice the day's average, so each pump is sized for the worst case: that hour on a hot, busy day, at the top of your temperature and swimmer ranges, with 20% on top. That is what the pump must deliver; the pump is then chosen so that this is no more than 70% of its capacity. The chlorine pump is sized without stabiliser, the larger need, so it covers either. Two minimums apply as well:
- The chlorine pump can feed at least 10 g of chlorine for every cubic metre of water the pool's filtration moves (2 g indoors), the German pool standard DIN 19643. We take a four-hour turnover.
- The acid pump gives at least 3 L/h for every million litres, enough to bring the pH back after a fill-up or a heavy day.
The size is the flow the pump must deliver against the pressure in the pool's return line.
Winter
For an outdoor pool we take winter water at about 18 °C, a fifth of the summer swimmers, and about a third of the summer sun. An indoor pool is heated and out of the sun, so its winter is taken as its summer.
Where the figures come from
- Chlorine used by each swimmer: Pool Water Treatment Advisory Group (PWTAG) conference, 2024; Berg et al., 2019.
- Chlorine lost to sunlight, with and without stabiliser: NSW Health, Public Swimming Pool and Spa Pool Advisory Document.
- Chlorine lost to warm water, and why pools need acid: Wojtowicz, Journal of the Swimming Pool and Spa Industry.
- Sizing for the busiest time, the sun, the warmest water and the most swimmers: Model Aquatic Health Code (MAHC), 2024, section 4.7.3.2.2.
- The least chlorine a feeder must deliver: DIN 19643, Treatment of water of swimming pools and baths.
- Dosing that turns down to a tenth: Western Australia, Code of Practice for the Design, Construction, Operation, Management and Maintenance of Aquatic Facilities.
These are estimates to plan with. Every pool is different: test the water and adjust, and call us on 1300 585 820 to check a pump for your site.