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.