Key takeaway: one litre of 12.5% liquid chlorine raises free chlorine by roughly 12 ppm per 10,000 litres of pool water, and 65% granular calcium hypochlorite needs about 15 grams per 10,000 litres for the same 1 ppm rise. Check your product’s actual strength first, since AU liquid chlorine ranges from about 10% to 12.5%, and correct alkalinity and pH before dosing, since both affect how well the chlorine works, not how much you need.
Most pools sit comfortably at 1 to 3 ppm free chlorine day to day, and get shocked up to roughly 10 ppm to clear algae, cloudiness or after heavy use. The chart below shows how much product that actually takes by pool volume, for the two most common Australian retail forms: liquid chlorine and granular calcium hypochlorite. For the wider basics of keeping pool water balanced, see our full pool water chemistry guide.
Chlorine Needed to Raise Free Chlorine by 1 ppm
| Pool volume | Liquid chlorine (12.5%) | Granular cal hypo (65%) |
|---|---|---|
| 20,000 L | 160 mL | 31 g |
| 30,000 L | 240 mL | 46 g |
| 40,000 L | 320 mL | 62 g |
| 50,000 L | 400 mL | 77 g |
| 70,000 L | 560 mL | 108 g |
Typical Shock Dose (Raising Free Chlorine by About 10 ppm)
| Pool volume | Liquid chlorine (12.5%) | Granular cal hypo (65%) |
|---|---|---|
| 20,000 L | 1.6 L | 310 g |
| 30,000 L | 2.4 L | 460 g |
| 40,000 L | 3.2 L | 620 g |
| 50,000 L | 4 L | 770 g |
| 70,000 L | 5.6 L | 1.08 kg |
How the Chart Works
Both figures come straight from the product’s labelled strength, not a fixed rule of thumb. Liquid chlorine at 12.5% contains 125 g of available chlorine per litre, so raising 10,000 litres by 1 ppm (1 mg per litre) needs 10,000 mg, or 10 g, of available chlorine: 10 g ÷ 125 g per litre = 80 mL. Granular calcium hypochlorite at 65% available chlorine (HY-CLOR) needs the same 10 g of available chlorine, but since it’s only 65% active: 10 g ÷ 0.65 = 15.4 g of product. Scale either figure to your own pool volume and target rise, and always check the actual percentage on your product’s label first, since strength varies by brand and form.
Worked example: to shock a 50,000 litre pool from 0 to 10 ppm with 12.5% liquid chlorine, that’s 10 × 400 mL = 4 litres. With 65% granular, it’s 10 × 77 g = 770 g. Add chemicals to water, never water to chemicals, and run the pump continuously for at least 24 hours afterwards.
Safety
Liquid chlorine and granular chlorine are both classified as hazardous, corrosive and oxidising products under SafeWork Australia and ADG Code criteria. Never mix chlorine with pool acid or any other chemical; the combination releases toxic chlorine gas. Store away from acid, dose in the evening with the pump running, and wear gloves and eye protection when handling concentrated product. For any exposure, call the Australian Poisons Information Centre on 13 11 26, available 24 hours a day.
More on Pool Water Chemistry
For the full picture of pool water balance, see our pool water chemistry guide. Related reading: how to shock a pool and when you actually need to, how to raise pH without overshooting it, and why your pool might be cloudy even after dosing correctly.
Frequently Asked Questions
How much chlorine do you need to shock a pool?
Can you put too much chlorine in a pool?
Do you put chlorine in a saltwater pool?
How long do you have to wait after adding chlorine before swimming?
What’s the difference between liquid, granular and tablet chlorine?
Sources
- HY-CLOR Australia – Granular Pool Chlorine (65% available chlorine)
- Standards Australia – AS 3633-1989 Private Swimming Pools: Water Quality
- Better Health Channel (Victorian Government) – Swimming pools: water quality
- Australian Government Department of Health, Disability and Ageing – Poisons Information Centre
