How to lower chlorine in a pool The short answer To lower chlorine in a pool, stop adding it: take the tablets out, or turn the salt cell down. Then take the cover off and let sunlight break it down — often a few ppm a day. For a fast drop, replace some of the water with fresh water, or use a chlorine neutralizer (sodium thiosulfate) exactly as its label says. Test before swimming.
Where your chlorine should be Free chlorine now
The chlorine that is working right now — it kills germs and algae.
Free chlorine you want
Good range: 2.3–12 ppm.
Type the size and your chlorine reading.
Step by step Test free chlorine and stabilizer (CYA): the right chlorine level depends on your stabilizer.
Stop adding chlorine — tablets out of the feeder, the salt cell turned down.
Uncover the pool and run the pump: sunlight breaks chlorine down.
In a hurry? Replace some water with fresh water, or use a chlorine neutralizer, following its label.
The product label always wins — if it says something different, follow the label.
Why it happens Chlorine usually runs high after a shock, a new bucket of tablets in the feeder, or a salt cell set too high for cool weather.
Stabilizer protects chlorine from the sun, so a well-stabilized pool loses chlorine more slowly.
Questions Is it safe to swim with high chlorine? Pool codes allow swimming up to 10 ppm free chlorine. Above that, eyes and skin get irritated — wait until it comes down.
How long does it take for chlorine to go down? In summer sun often a few ppm a day; under a cover or indoors, much slower.
What should my chlorine level be? At least 7.5% of your stabilizer (CYA) level, and ideally about 11.5% — with CYA 40 that is 3 ppm at the least and about 5 ppm to aim for.
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