How to Lower Chlorine in a Pool. Lowering the chlorine content in a pool is sometimes necessary to maintain a safe and effective level. The ideal chlorine level is 1.5 to 3.0 parts per million (PPM). In this range, chlorine is a great disinfectant, but when the level is too high, it destroys the pool's chemical balance, is unsafe for swimming and can even damage pool equipment. Here's how to quickly and safely lower the chlorine level.
Use an approved titration test kit to determine the concentration of chlorine. If you know the level is high, but the test solution colors, and then quickly goes clear, you may need to dilute the pool water sample with distilled water to get an accurate reading. Follow the kit's instructions to accurately measure extremely high levels.
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Calculate how many gallons of water your pool holds. The formula is average width times average length times average depth times 7.5. This will give you the total gallons of water in your pool. The pool capacity will determine how much neutralizing chemical you will add to lower the pool's chlorine level.
Neutralize the chlorine with sodium thiosulfate. See the Resource section for a calculator to determine the amount to use to return the pool water to the ideal chlorine level.
Dilute the required amount of sodium thiosulfate in a 5-gallon bucket of water and walk around the pool, pouring evenly as you go. Keep the circulation system operating for at least two hours to mix the solution thoroughly, and then retest the water to verify you have reduced the chlorine concentration to a safe level.