There are many different issues that pool owners will learn to acquaint themselves with during pool ownership. One of the more rare but frustrating problems that pool owners face is an issue called a “chlorine lock.” There is a lot of debate about chlorine locks – some people say it isn’t a real issue – but pool owners who have had to deal with it know otherwise. In this guide, we will introduce what a chlorine lock is and the best way to address the problem.
What is a chlorine lock?
In short, a chlorine lock is a phenomenon that occurs when you add too much cyanuric acid (pool stabilizer) to your pool. As we have discussed in other articles, cyanuric acid (CYA) is often used in tandem with chlorine as a means to help protect the chlorine from the sun. UV rays from the sun will break down chlorine very quickly without a pool stabilizer, which renders it unable to sanitize the water.
Cyanuric acid, in essence, helps protect chlorine from being degraded by sunlight. That all sounds good, so where is the problem? Well, too much of it can have the opposite effect, breaking the chlorine down and rendering it useless as a sanitizer for your pool. This also means that your pool will have an improper chemical balance and it might not be safe to swim in.
Signs of a chlorine lock
Now that you know what a chlorine lock is, it is time to learn about the signs that you are dealing with this problem. One of the most common signs is an intensely bleachy smell. Most people would assume that a pool that smells strongly of bleach may have had an overshoot of chlorine, but this is not the case. There are substances called chloramines which produce this smell. Chloramines are the result of improperly treated water. It might seem counterintuitive, but this smell usually indicates that you have too little active chlorine, not too much.
Fixing a chlorine lock
The first thing you want to do if you notice the intense smell of chloramines is to test your water. This will help confirm the problem as a chlorine lock. Ideally, free and total chlorine should be roughly equal. It will also alert you if there are any other issues with your chemical balance before you start to address the chlorine lock.
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The problem with a chlorine lock is that attempts to add more chlorine to the water to raise the levels of free chlorine will likely just compound the problem. You have to remove some of the pool stabilizer from the pool to bring the levels back to such a point that the chlorine can remain active again. The easiest way to do this is to do a partial drain of your pool. Draining about a quarter of the water off and adding freshwater is often enough to break the chlorine lock, allowing you to readjust your chemicals accordingly.
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Sometimes, if the problem is bad enough, one partial drain will not be enough to correct the problem. Be sure to test your water after it has been drained and refilled. It might take a few partial drains to fix the problem if it got too far out of control.
Another option for fixing a chlorine lock is to shock the pool, but not with chlorine. There are a few different non-chlorine options available. These non-chlorine shocks work to oxidize the water, which will make it cleaner and should break the shock, allowing you to fix your chlorine levels manually. There is a simple formula that will help you determine how much of this non-chlorine shock to add to your pool:
(Total Chlorine – Free Chlorine) x (total pool volume/1,000) x 2
There are several places online that have free calculators you can use to determine how much you need to add if you don’t want to work out the formula yourself.
As odd as it sounds, doing a chlorine shock can also fix the problem. What is needed when dealing with a chlorine lock is to reach a chlorination breakpoint. Shocking with chlorine will spike the levels of the chemical in your pool, which will allow the chlorine to break the chemical structure of chloramines, which keeps chlorine inactive in the water. For this to work properly, you will need to make sure that your pH is in proper balance before the shock. You want your pH to be between 7.3-7.6.
There is a bit of debate about how much shock is needed to reach that chlorination breakpoint, but many pool experts agree that performing a regular shock according to the manufacturer’s instructions is often enough to break the lock. You will want to let the pool sit overnight and test the water in the morning to determine whether or not the efforts were successful. You may need to shock it again.
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Sometimes shocking, whether with non-chlorine or chlorine shock, is ineffective. In this case, it is advised that you try the partial drain method. If problems continue or this doesn’t work to break the lock, it might be time to call in a professional. When these problems get out of control, sometimes the only solution is to have an experienced pool tech come out to get the problem fixed.
Wrapping Up
Regardless of the method you choose to break the lock, it is important to understand what it is and how to address it. When the chlorine in your pool is rendered inactive, it means that it cannot properly sanitize the water and will not only lead to an icky smell of chloramines but will also render the water unsafe to swim in. Problems like a chlorine lock can be highly frustrating if you don’t understand the problem and the methods you can use to address it. Any one of the solutions we discussed in this article can be effective for breaking a chlorine lock. It is up to the pool owner to determine which efforts they wish to try first.