How to Get the Chlorine Level Down in a Pool

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Things You'll Need

  • Pool test strips

  • Sodium thiosulfate

Attain normal levels of chlorine before swimming.

Chlorine is the most common chemical used in the treatment of swimming pools. It can be added to the water as a solid, liquid or gas. It destroys harmful pathogens and destroys other impurities through sanitation and oxidation. Swimming pools need to be super-chlorinated or shocked on occasion to completely oxidize and get rid of the impurities. This process raises free chlorine levels from the normal range of 1 to 3 parts per million (ppm) up to 8 to 10 ppm. Swimmers should always wait until the chlorine level returns to normal before swimming.


Step 1

Turn off the automatic chlorine feeder and remove any floaters containing chlorine tablets. Do not add any additional chlorine.

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Step 2

Open the cover of the swimming pool. Chlorine is degraded by the sun's ultraviolet rays and will naturally disperse into the air.

Step 3

Allow time for the chlorine to combine with contaminants in the pool. Chlorine levels will decrease within 24 hours.

Step 4

Check cyanuric acid level with pool test strips. If it is above 100 ppm, drain the pool partially and refill with clean water.


Step 5

Add sodium thiosulfate if the chlorine levels are not lower after 24 hours or if they are consistently above 5.5 ppm with cyanuric acid levels of 30 to 95 ppm. Add one pound of sodium thiosulfate per 100,000 gallons of water to lower chlorine by 1ppm.


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