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Chlorine Lock: what you should know about it

The Complete Guide to Chlorine Lock

Heard the term ‘chlorine lock’ and want to know what it means? Wondering how you can break a chlorine lock? Or perhaps how to avoid it in the first place? We are going to tell you everything that you need to know on this page!

What is a Chlorine Lock?

As you know, when you add chlorine to the water, you will also need to add a stabilizer called cyanuric acid. The purpose of this stabilizer is to prevent the chlorine from breaking down under UV rays. When you add the right amount of stabilizer to the water, it should provide just enough protection for the chlorine to ensure that the chlorine remains in the water, but not so much protection that it prevents the chlorine from doing its job.

A chlorine lock occurs when you add too much cyanuric acid to the pool. When this happens, the chlorine can’t do its job. It can’t break down bacteria and some organic matter in the pool. There may be just enough free chlorine to clean up some of it, but not so much that your pool will be completely rid of bacteria. Your chlorine becomes ‘locked’ and unable to function.

It is important to note that when a chlorine lock occurs, the amount of stabilizer in the water will not change. Cyanuric acid doesn’t disappear in the same way that chlorine does. Once it is there, it is there. The only real option that is guaranteed to work is to drain the stabilizer away. More on that in a short while, though.

Does Chlorine Lock Actually Exist?

You will see a lot of pool experts claim that the idea of ‘chlorine lock’ does not exist. It does. Perhaps one of the main reasons why a lot of these experts claim it doesn’t exist is simply because chlorine lock can be caused by a multitude of different issues with the pool. Therefore, they prefer to refer to individual issues rather than the blanket term.

Why is a Chlorine Lock a Bad Thing?

The problem with a chlorine lock is that there is no longer going to be enough active chlorine in the water to completely eliminate the bacteria in the water. It won’t matter how much chlorine you add, it can be tough to get back on track.

However, it is unlikely that you will notice that there is not enough active chlorine unless you are testing for it. After all, there will be just enough chlorine in the water to break down organic matter and keep the water looking fairly clean, but there won’t be enough to actually filter out the bits and pieces that are likely to make you sick.

A lot of people with a swimming pool dealing with a chlorine lock are unlikely to know that a chlorine lock has actually occurred. They will just keep adding chlorine to the water, none the wiser that by doing so, they are not really making the problem any better.

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How Do You Know When You are Dealing with Chlorine Lock?

Simple. You have to smell the water.

If you walk past your swimming pool and it smells of bleach, then there is a pretty good chance that a chlorine lock has happened. This smell comes from a compound known as chloramines. If you smell the bleach smell, it doesn’t mean that your pool is clean. In fact, it means the complete opposite. It means that your chlorine is not working properly. When your chlorine is not cleaning the pool, these chloramines start to build-up. It is pretty much the first sign that you will get that you are dealing with a chlorine lock.

If you suspect that your pool is in the midst of a chlorine lock, then you do need to test the water. This will be your standard chlorine test. You are looking for total chlorine and free chlorine levels. These numbers need to be the same. If the total chlorine level is higher than the free chlorine level, then this means that you are dealing with a chlorine lock.

How Can You Avoid a Chlorine Lock?

If you deal with bromine instead of chlorine in your swimming pool, then you will never need to deal with a chlorine lock. This is because bromine doesn’t break down in the heat or under UV rays. As a result, you do not need to use a stabilizer. 

Of course, you could always take extra precautions when adding chlorine and stabilizer to the water. Granted, this is not something that will prevent every single case of chlorine lock. In some cases, there is simply going to be nothing that could have prevented it from happening. However, we can assure you that if you take greater care in adding chemicals to your water, the chances of chlorine lock occurring will plummet. Of course, this means ensuring that the PH level of your water is fine.

Don’t forget; you will also want to regularly check the water for chemical levels. You can then make adjustments as needed. This may be enough to prevent the chlorine lock from happening in the first place.

How Do You Fix a Chlorine Lock?

Thankfully, there are a few different methods for dealing with a chlorine lock. These are methods that have been proven to work. Some of them may work a little better than others. For example; some of these methods may actually deal with the chlorine lock completely, while others are going to be more of a band-aid for the issue.

Draining a little bit of the pool away and then refilling it

This is probably going to be the simplest method for breaking a chlorine lock. It also allows you to add a little bit of clean water to your pool. This is something that you should be doing on occasion anyway, so what is the harm?

The amount of water you drain away is up to you. Most people who are looking to break a chlorine lock will try to get rid of at least a quarter of it. We have seen some people drain their entire pool. In our opinion, the more you drain from the pool, the better. After all, draining the water away will remove some of the stabilizers. This is exactly what you want to happen.

Once you have drained the water away, refill the pool up to the required levels and try to get the chemical balance right again. If you can’t, then there is a good chance that you may need to drain even more water from the pool. This is why it is important that you are not draining only a little at a time. The less you drain, the more you will need to repeat this process. If you drain at least a quarter of the water away, chances are that you are going to get it right the first time…unless you have really overdone the amount of stabilizer in the pool.

Using a chlorine shock

If you do not feel like draining anything from your pool, then you may find that giving the pool a chlorine shock is sufficient. You do not have to do anything special here. Just follow the instructions that come with the chlorine shock you have purchased and it should be fine.

The purpose of the chlorine shock is to break down the chloramines. Once they have broken down, the chlorine should have free reign to start breaking down bacteria and working properly again.

That being said, some people will see adding a chlorine shock as a ‘band-aid’ solution. You aren’t really reducing the amount of stabilizer in the pool, you are just overwhelming it with chlorine. If the issue is minor, then this may be all that is required to correct the problem. However, if the free chlorine levels are seriously out of balance, then draining your pool is probably going to be the better solution.

Remember; you shouldn’t be using your pool for at least 24-hours after the chlorine shock. Once the 24-hours has passed, you can check to see if the chlorine lock has been broken. If it hasn’t, then you can try shocking again or, better yet, draining the pool.

Using a Non-Chlorine Shock

Some people will find that a non-chlorine shock is a far better method for dealing with a chlorine lock. However, they tend to avoid it because it does involve a little bit of maths.

You will need to know the following information in order to carry out a non-chlorine shock:

  • Total chlorine levels
  • Free chlorine levels
  • The size of your pool in gallons

Once you have this information, carry out this equation:

(Total Chlorine – Total Free Chlorine Levels) x (Gallons of Water in Pool Divided into 10,000)

You then multiply this figure by 2. This will tell you exactly how much non-chlorine shock to add to the pool. It is vital that you get this information right, otherwise, it will be difficult to break the chlorine lock! You may need to repeat the process several times, but you should never add more non-chlorine shock than the equation suggests. 

Remember; a chlorine lock can be tricky to deal with. However, it is something that you will need to deal with sooner as opposed to later. We promise that at least one of the three methods detailed on this page will help to break the lock, allowing you to swim happily in your pool again!

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