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How to Treat Chlorine Lock in a Swimming Pool

How to Treat Chlorine Lock in a Swimming Pool. While some pool experts believe chlorine lock doesn't exist, others recognize that an imbalance in your swimming pool chemicals results in problems with the pool's water. Chlorine lock results when insufficient water replacement allows the build-up of cyanuric acid (CYA), often called a stabilizer.

Test your swimming pool chemicals before you do anything. In theory, chlorine lock occurs when the pH level of your swimming pool becomes unbalanced. The level of free chlorine, the unbounded portion of chlorine in your pool, rises to an abnormal level, indicating the chlorine's inability to perform correctly.

Shock your swimming pool by adding an oxidizer to the swimming pool. There are several oxidizers you can use to shock your pool, but you should avoid adding chlorine which works to shock pools with non-chlorinated problems. Instead, add bleach, hydrogen peroxide or potassium peroxymonosulfate.

Backwash your filtration system to increase the level of fresh water in your swimming pool. Most multiport valves contain a setting to backwash the system. You need to alternate between the backwash and rinse settings on the multiport valves until the water runs clear or you feel an adequate amount of fresh water entered the pool.

Add fresh water to your swimming pool. Partially drain the swimming pool, keeping in mind that a draining the pool too much can result in damage if you don't do it correctly. Allow fresh water to fill the pool to the proper level of water.

Adjust the swimming pool's pH level according to test results. You may need to adjust the swimming pool chemicals to achieve the correct pH balance after you add fresh water to the pool.

Correct Chlorine Lock In Your Swimming Pool

Chlorine lock or stabilizer lock is a term used inaccurately and inappropriately by many uneducated providers of pool advice, service and chemicals. Contrary to the myth that too much stabilizer, most commonly cyanuric acid, or CYA, locks the chlorine to be unavailable and causes algae bloom, stabilizer is a critical part of the important Oxidation/Reduction Potential, or ORP, for the pool to maintain effective sanitation. Temperature, pH, stabilizer level and calcium concentration all have to be measured to make the proper adjustments to the pool chemistry. Measure the pool temperature and record. Divide the number of gallons in the pool by 120,000. Look up the minimum chlorine level in parts per million based on the pool's temperature and CYA level. Also, calculate the chlorine breakpoint for superchlorination. Subtract the free chlorine from the total chlorine and the remainder is the combined chlorine. See chart 2 "Avoiding Algae in Chlorinated Swimming Pools." For bleach, the conversion is 2 gallons per pound of "pure" chlorine (assumes 6 percent sodium hypochlorite solution).


You only need to use on of Step 2, 3, or 4, not a combination.

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