How to Bring Down Chlorine in a Pool
Chlorine is often added to swimming pools in large quantities for hygienic reasons. After this treatment, the chlorine concentration must be brought back down to a level that is suitable for swimmers. You can do this in one of three ways: you can allow the chlorine to break down naturally over a period of days, which typically takes between 2 and 20 days depending on local weather conditions and on how much excess chlorine is in your pool; you can replace part of the pool water with fresh water from the tap; or you can neutralize the excess chlorine with chemicals, which is described here. Does this Spark an idea?
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Things You'll Need
- Pool chlorine testing kit
- Sodium thiosulfate or other chlorine neutralizing reagent
Instructions
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Test the chlorine level in your pool. Collect your test sample water from the pool's deep end, away from the filter inlet, at least one foot below the water's surface. According to the Water Quality and Health Council, the free available chlorine level should be maintained between 2.0 and 4.0 parts per million (ppm), and should never fall below 1.0 ppm. If it's higher than 4.0 ppm, you can proceed with chlorine reduction.
If the chlorine level is very high, it may not show up correctly on your testing strip. If this is the case, you can dilute another sample of pool water with four parts distilled water, then test that, and multiply the chlorine reading by five. This will give you the correct chlorine concentration value for your pool.
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Determine the correct amount of chlorine neutralizing reagent to add to your pool. This will depend on the chlorine concentration you just measured and on your pool's gallonage. There should be instructions on the reagent's container for determining the correct amount. Sodium thiosulfate is commonly used for this purpose, as it bonds with the chlorine and renders it neutral. (Other sulfur-based chemicals include sodium sulfite and sodium metabisulfite.) Commercially, chlorine neutralizers are often called "after shock" or something similar, because "shocking" is the term used for increasing a pool's chlorine level.
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Pour the neutralizing reagent around the perimeter of the pool, especially at the deep end. Don't use too much, as this will cause the free chlorine level to drop too low and any extra chlorine you might add to restore the balance will simply be neutralized, until all of the neutralizing reagent is used up.
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Run your pool filtering system for at least four hours after treatment, in order to evenly distribute the neutralizing reagent throughout the pool. Don't swim in the pool until the chlorine concentration returns to a suitable level.
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