How to Lower Pool Chlorine: Neutraliser Dose, Free vs Total

Name: comparepoolquotes
Price range: $$$

To lower pool chlorine, stop adding it and let sunlight and time bring it down, or neutralise it: product labels give 10 g of sodium thiosulfate per 10,000 litres per 1 mg/L, so a 50,000 L pool from 10 to 3 mg/L takes 350 g. Test free and total first: high total with low free needs more chlorine, not less.

The short answer

Neutraliser dose: grams = drop in mg/L × litres ÷ 10,000 × 10. Two Australian product pages (one maker, one retailer) give 10 g per 10,000 L per 1 mg/L. Add half, run the pump an hour, retest.
Free vs total: total chlorine is free plus combined (HealthyWA, NSW Health). If total is high but free is normal or low, the excess is chloramine; a neutraliser removes the free chlorine you need and, a retailer label says, not the chloramine.
When it is too high to swim: above 4 mg/L free after a shock (SA Health); above 10 mg/L total, the public-pool maximum in NSW and Queensland. Home range: 1.0–3.0 mg/L.
A strong chlorine smell means too little, not too much, HealthyWA says.
Overdosing neutraliser leaves no chlorine: one retailer label warns it can make chlorine extremely difficult to build back up. In a salt pool, turn the chlorinator down first.

The free-vs-total decision table: what each chlorine reading means and whether to lower it (health-department limits read 18 October 2026; public-pool figures labelled; home figures from SA Health and HealthyWA)
Reading	What it means	Limit and source	What to do
Free 1.0–3.0 mg/L, combined under 1.0	In range	SA Health home range 1.0–3.0, ideal 2	Nothing. Do not neutralise
Free 3–4 mg/L in a stabilised outdoor pool, water above 26°C	Not high	HealthyWA minimum for that pool is 3 mg/L	Nothing; this is the floor, not an overdose
Free above 4 mg/L after a shock dose	Too high to swim	SA Health: do not use the pool until free chlorine falls to 4 mg/L	Wait, usually overnight, or neutralise the excess
Total above 10 mg/L	Above the public-pool maximum	NSW Regulation and Queensland Health: total chlorine max 10 mg/L	Neutralise to below 10; Queensland Health names sodium thiosulphate for this
Total minus free above 1.0 mg/L (combined chlorine)	Chloramines, not too much chlorine	Public-pool max 1.0 mg/L (NSW, Queensland; Queensland ideally under 0.2)	Do not neutralise. Raise free chlorine to 10 times the combined reading (NSW Health)
Fresh Sydney mains water: total about 1, free near zero	Chloramine from the tap	Sydney Water typical at taps, Apr–Jun 2026: monochloramine 0.88–1.16 mg/L, free 0.04	Chlorinate normally; the reading is the tap water

How do I lower the chlorine in my pool fast? The neutraliser dose

Sodium thiosulfate is the chemical sold as chlorine remover, reducer or neutraliser. NSW Health’s 2026 guidelines define it as a chemical that can be added to water to neutralise all residual chlorine, and Queensland Health’s guidelines use it to bring total chlorine back under 10 mg/L after hyperchlorinating a public pool.

Test free and total chlorine with a kit that reads both. Use the decision table above first.
Turn off the source. Switch the salt chlorinator off or right down, remove floaters and feeders.
Work out the dose: grams = (reading − target) × pool litres ÷ 10,000 × 10. Two Australian product pages, one maker’s (a 985 g/kg product) and one retailer’s, both give 10 g per 10,000 L per 1 mg/L.
Add half, dissolved in a bucket of pool water, with the pump running. The retailer label says pre-dissolve on fibreglass to avoid staining.
Wait an hour and retest (the retailer label’s interval), then dose the rest from the new reading.

Worked example. A 50,000 L pool reads 10 mg/L free after a shock and you want 3: 7 × 50,000 ÷ 10,000 × 10 = 350 g. Add 175 g, wait an hour, retest.

Pool volume	Lower by 1 mg/L	Lower by 3 mg/L	Lower by 7 mg/L
30,000 L	30 g	90 g	210 g
50,000 L	50 g	150 g	350 g
70,000 L	70 g	210 g	490 g

The half-dose rule: neutralise half the excess, retest, then the rest, because an overdose leaves the pool with no chlorine at all. The retailer label warns that too much makes chlorine extremely difficult to build back up later.

Free vs total chlorine: which one is high?

Pool kits report two numbers. HealthyWA: free chlorine is the chlorine not bound to wastes; chlorine combined with wastes is combined chlorine; total chlorine is the sum. NSW Health’s 2026 guidelines say combined chlorine (chloramines) is a weaker disinfectant and can cause skin and eye irritation and a strong, offensive chlorine odour.

So subtract: total minus free is combined. If that is above 1.0 mg/L, the public-pool maximum in NSW and Queensland, the pool does not have too much chlorine; it has too little free chlorine to burn the chloramines off. NSW Health’s fix is breakpoint chlorination, shock dosing to at least 10 times the combined chlorine concentration. A neutraliser is the wrong tool here; one retailer’s chlorine-remover label says it does not remove chloramines or combined chlorine. HealthyWA says a strong chlorine smell is caused by too little chlorine rather than too much.

One Sydney catch: the tap water itself is chloraminated. Sydney Water’s April–June 2026 reports show typical monochloramine at customers’ taps of 0.88 mg/L (Potts Hill) and 1.16 mg/L (Prospect East), with free chlorine 0.04. A top-up straight from the hose can therefore read as combined chlorine, and NSW Health notes that diluting with drinking water does less where the supply carries a chloramine residual.

The free-versus-total rule: neutralise only when free chlorine is high; when total is high and free is not, add chlorine. Raising it is covered on how to raise pool chlorine.

How to lower pool chlorine without chemicals

If nobody needs to swim today, stop adding chlorine and let it fall. NSW Health says sunlight breaks down chlorine in outdoor pools, so leave a solar or leaf cover off and run the pump; stabiliser slows this, because protecting chlorine from sunlight is its job. In a salt pool, lower the chlorinator output or hours rather than switching it off for days; the chlorinator troubleshooting page covers the settings, and how long a pool pump should run the pump.

How fast it falls depends on sun, temperature, stabiliser and how many people swim; we found no Australian health department that publishes a decay rate, and one retailer says that in cooler weather it can take days or weeks. Partial draining also works, by the share you replace, but it costs water and, in Sydney, adds chloramine.

When is the chlorine too high to swim?

SA Health’s home figures: 1.0–3.0 mg/L free chlorine, ideal 2; after a shock dose, do not use the pool until free chlorine falls to 4 mg/L. In a stabilised outdoor pool, HealthyWA’s minimum is 2 mg/L below 26°C and 3 mg/L above, so 3 or 4 in summer is not an overdose. Public pools must stay at or under 10 mg/L total chlorine. HealthyWA also says to allow at least 30 minutes after adding any chemical. The full swim-or-wait table is on can you swim in a pool with algae, and this page does not repeat it.

If chlorine keeps overshooting because a chlorinator is running too long or is oversized for the pool, pool equipment explained lists what a quote should state; compare pool quotes with the unit named by model and rated volume.

Common questions

How do I lower the chlorine in my pool fast?

Add a sodium thiosulfate chlorine neutraliser: 10 g per 10,000 litres for each 1 mg/L, on one Australian maker’s product page. Add half, run the pump an hour, retest.

How do I lower total chlorine in my pool?

Check free chlorine first. If free is normal and total is high, the difference is combined chlorine; NSW Health’s 2026 guidelines control it by shock dosing to 10 times the combined level, not by neutralising.

How long does it take for chlorine to go down in a pool?

It varies with sun, heat, stabiliser and use; no health department publishes a rate. After a shock dose SA Health says waiting for 4 mg/L may mean leaving the pool overnight.

Is 5 ppm chlorine too high to swim?

On SA Health’s home guidance, yes: do not use the pool until free chlorine is 4 mg/L or less after shock dosing. The routine home range is 1.0–3.0 mg/L.

Why does my pool smell of chlorine if the level is high?

HealthyWA says the smell is caused by too little chlorine rather than too much. Test total and free: the gap is chloramine.

Sources

General information only, current at 2026-10-18. Pool rules differ by state and by council, and penalty amounts are updated regularly. Confirm your own obligations with your council or a registered inspector before acting.