Pool chlorine calculator (Australia)
To lift free chlorine by 1 ppm in a 40,000 litre pool, add 320 mL of 12.5% liquid chlorine or 61 g of 65% granular chlorine.
Rule of thumb: 80 mL of 12.5% liquid chlorine per 10,000 litres raises free chlorine 1 ppm. Australian test kits read in mg/L, which is the same number as ppm.
Chlorine doses by pool size
| Pool size | 12.5% liquid, +1 ppm | 65% granular, +1 ppm | Shock to 16 ppm, liquid |
|---|---|---|---|
| 20,000 L | 160 mL | 31 g | 2.4 L |
| 30,000 L | 240 mL | 46 g | 3.6 L |
| 40,000 L | 320 mL | 61 g | 4.8 L |
| 50,000 L | 400 mL | 77 g | 6 L |
| 60,000 L | 480 mL | 92 g | 7.2 L |
| 75,000 L | 600 mL | 115 g | 9 L |
What is on Australian shelves
Liquid chlorine here is 12.5% sodium hypochlorite, sold in 15 L and 20 L drums — Hy-Clor and Lo-Chlor through the hardware chains, BioGuard and Zodiac through pool shops. Granular chlorine is calcium hypochlorite at 65% to 70%, and the stronger tub goes further per kilo than the label price suggests. Liquid chlorine loses strength on the shelf, several percent a month in summer heat, so buy the size you will use within a few weeks rather than the one that is cheapest per litre.
Stabiliser and the Australian sun
Unstabilised chlorine is gone within hours under a January sun. Keep cyanuric acid between 30 and 50 mg/L and hold free chlorine at roughly 7.5% of that reading — about 3 mg/L at a stabiliser level of 40. Granular and tablet chlorine add stabiliser with every dose, so a pool run on those alone climbs past 100 mg/L within a season and the chlorine stops working at any sensible level. Liquid chlorine adds none, which is why pool shops move you onto it once stabiliser is where you want it.
Through the season
Demand peaks from December to February, when an uncovered pool can lose 3 to 4 mg/L a day. Through winter, from May to August, a pool held at 1 to 2 mg/L costs very little to keep clear, and clear water in September is far cheaper than recovering a green one. Test twice a week in summer and once a fortnight in winter.
More calculators
Not sure how many litres your pool holds? Measure it in metres with the pool volume calculator in litres. For a green pool use the pool shock calculator, and for stabiliser see the CYA calculator. The chlorine dosing calculator is this same maths with US units in front.