Chlorine lock refers to a common pool maintenance problem that often occurs in swimming pools where the chlorine in the pool is rendered inactive, even though you may have plenty of chlorine in the pool. In essence, a chlorine “block” means that the chlorine in the pool is literally being blocked from doing its job by other chemicals.
How chlorine blocks happen
One of the main reasons that chlorine can become ineffective is that too much stabilizer has accumulated. Stabilizer (cyanuric acid) can build up over a long period of time, sometimes months or even years. Once it reaches a high enough level the chlorine is rendered useless.
How to fix a chlorine block
The only way to break the lock is to reduce the level of cyanuric acid in the pool, and the fastest way to accomplish this is to add fresh water to the pool. This will help dilute the acid levels in the pool so that the chlorine will become more effective.
Adding fresh water can usually be done by performing large backwashes. However, if this doesn’t correct the problem you may need to partially drain and replace the water in the pool.
Preventing future blocks
It is important to keep a close eye on the ph levels in your pool. Measure the pH daily to ensure that the proper levels are maintained. Keep in mind that many things can factor into changes in pH levels in your pool. For example, excessive sunlight and heat can drastically change the pH of the water. It can also be changed if a lot of rainwater has been allowed to enter the pool.
When you keep a good watch on your pool you’ll know when to add the proper chemicals to maintain crystal clear water. The recommended pH level is typically held at 7.4 to 7.6, which is slightly alkaline. When you have water that is too acidic, below 7 pH, it can erode the plaster surface. When water is too alkaline, above 8 pH, it can increase the instance of stains and scale. Perfectly balanced or neutral water is 7.0 pH.