How to Lower Chlorine in a Pool: 5 Safe Methods
Too much chlorine makes a pool unpleasant: stinging eyes, itchy skin, a harsh smell and faded swimwear. Over time it can also damage liners, fittings and equipment. The good news is that high chlorine nearly always falls on its own once you stop adding more, and there are safe ways to speed it up. Here is how to lower chlorine in a pool, starting with the easiest methods.
First, confirm chlorine really is too high
Test both free chlorine and total chlorine. Free chlorine is the active sanitiser. Total chlorine minus free chlorine gives combined chlorine (chloramines), the spent chlorine that causes the strong “pool smell” and red eyes.
- High free chlorine: you have too much chlorine. Follow the steps below.
- Strong smell but low free chlorine and high combined chlorine: you actually need more chlorine to burn off the chloramines. See how much chlorine to shock a pool.
- Green water with high chlorine: the problem is usually stabiliser, pH or filtration rather than chlorine. Read pool is green but chlorine is high.
What chlorine level is normal?
Many home pool owners aim for about 1 to 3 mg/L (ppm) free chlorine, with pH 7.2 to 7.6. For comparison, Queensland Health’s water quality guidelines for public aquatic facilities recommend at least 1.0 mg/L free chlorine for pools without cyanuric acid and at least 2.0 mg/L for outdoor pools with cyanuric acid. They also set a maximum of 10 mg/L total chlorine and a pH range of 7.2 to 7.8. Outdoor pools with stabiliser need a little more free chlorine to work, so do not chase chlorine too low.
How to lower chlorine in a pool: 5 methods
1. Stop adding chlorine
Stop dosing liquid chlorine, remove chlorine tablets from floaters and skimmers, and turn down or pause your salt chlorinator output. In a salt pool, an output set too high or a long run time is the most common cause of high chlorine. This step alone fixes most cases within a few days.
2. Let the sun do the work
UV light breaks down chlorine quickly. Remove the pool cover and run the pump during the day. Unstabilised chlorine drops fastest; pools with high cyanuric acid (stabiliser) lose chlorine more slowly.
3. Aerate and circulate
Run the pump and filter longer, and point return jets upward to agitate the surface, or run water features. This helps chlorine gas leave the water and keeps the water evenly mixed so your test results are accurate.
4. Partially drain and refill
Replacing some water with fresh water lowers chlorine in direct proportion: replace 20% of the water and chlorine falls by about 20%. It also dilutes stabiliser and dissolved solids. Check local water restrictions first, and know where pool water can legally be discharged.
5. Use a chlorine neutraliser
For the quickest result, a chlorine neutraliser such as sodium thiosulphate reduces chlorine within hours. Dose carefully by the product label, in small steps, because overdosing can leave you with no chlorine and an unprotected pool. Retest after a few hours.
How long does it take for chlorine to drop?
With dosing stopped and sun exposure, a few ppm usually drops within one to three days, depending on sunlight, temperature, stabiliser level and swimmer load. Dilution and neutralisers work within hours. Test daily until you are back in range.
Is it safe to swim with high chlorine?
Slightly high chlorine is uncomfortable rather than dangerous for most people, but very high levels can irritate eyes, skin and airways. The safest approach is to wait until free chlorine is back within your normal range before swimming, especially for children. For public pools, Queensland Health’s guidelines set a maximum of 10 mg/L total chlorine.
Myths and mistakes
- “Baking soda lowers chlorine.” It does not. Bi-carb soda raises total alkalinity and slightly raises pH; it has no direct effect on chlorine.
- “Shock it to fix the smell.” Only if combined chlorine is high and free chlorine is low. Shocking a pool with high free chlorine makes things worse.
- “More chlorine means cleaner water.” Above the right range it just irritates swimmers and wastes money.
- Ignoring pH. High pH makes chlorine weaker, which tempts owners to add more. Keep pH balanced with hydrochloric acid (added separately from chlorine) and see how much acid to add to a pool.
- Never mix chlorine and acid in a bucket or container. This releases toxic chlorine gas. See our liquid chlorine safety tips.
How to stop chlorine getting too high again
- Test two or three times a week in summer and after heavy use, rain or a shock dose.
- Calculate doses from your actual pool volume. With 12.5% liquid chlorine, about 80 mL raises free chlorine by 1 ppm per 10,000 litres. See our 12.5% liquid chlorine page for a dosing table.
- Set salt chlorinator output to suit the season, and keep the cell clean: how to clean salt chlorinator cells.
- Keep stabiliser moderate; read cyanuric acid in swimming pools.
- Check that your chlorine level targets match your pool type.
Frequently asked questions
How do I lower chlorine in my pool quickly?
The fastest options are a chlorine neutraliser such as sodium thiosulphate, dosed carefully by the label, or partly draining and refilling with fresh water. Stopping chlorine dosing and exposing the pool to sun also works, usually within one to three days.
Will baking soda lower the chlorine level in a pool?
No. Baking soda (bi-carb soda) raises total alkalinity and slightly raises pH. It does not lower chlorine.
What is the highest chlorine level that is safe to swim in?
Most home pools aim for about 1 to 3 ppm free chlorine. Queensland Health guidelines for public pools set a maximum of 10 mg/L total chlorine. If levels are well above your normal range, wait until they fall before swimming.
Why is my pool chlorine too high?
Common causes are overdosing liquid chlorine or tablets, a salt chlorinator set too high or running too long, and a recent shock dose. Low sunlight can also slow the natural breakdown.
Should I shock the pool if chlorine is high?
No. Only shock if combined chlorine is high and free chlorine is low. Shocking a pool that already has high free chlorine makes it worse.
How long does it take chlorine to go down?
With dosing stopped and good sun exposure, a few ppm usually drops in one to three days. Dilution and neutralisers work within hours.