Chlorine lock is one of those pool terms that is pretty misunderstood among pool owners, while some experts even try to discredit it as a sales gimmick.
But having experienced the phenomena myself, I know that chlorine lock exists and it can be a pain to correct.
So in this post, we’re going to go over what chlorine lock actually is, some signs to look out for to see if you have it, and how to actually fix it.
Let’s dive right in!
What is chlorine lock?
Chlorine lock is what sometimes can happen when you have added too much pool stabilizer, or CYA, to a pool.
CYA (cyanuric acid) is a chemical intended to protect the chlorine molecules from being eaten up by UV rays too quickly, and if you get too much of it, it can completely block your chlorine and render it useless.
Signs you have chlorine lock
Have you ever walked out to your pool area or the public pool and caught a whiff of that strong bleachy smell?
It would seem like this would be the result of adding too much chlorine to the pool, right?
When your pool has that chemical smell, it is in fact chloramines, which are “chemical compounds that build up in pool water when it is improperly treated.”
There are several reasons for the build-up of chloramines, but a lot of times this means you have chlorine lock.
The problem with the chemical smell of chloramines is that a lot of pool owners mistakenly think they have too much chlorine, so they either drain some water out of the pool or quit adding the chemical for a few days.
But what it actually means is that you don’t have enough chlorine or that it isn’t active.
The other thing people do is test the water and determine they need to add chlorine.
However, every time they test the water, it keeps reading low, no matter how much chlorine they add. This means that your CYA has it locked up.
Under normal conditions, total chlorine and free chlorine should equal each other, but if you’re experiencing chlorine lock, they will be unequal.
>>Read: How to choose the best pool testing kit
It’s important to test your water before deciding to take the steps to correct chlorine lock, so that you don’t throw your pool chemistry even further out of balance and end up having to drain more of the pool water than you’d like.
>>Read: How to balance your pool water
How to fix chlorine lock
If your test results show that you likely have chlorine lock, there are a few ways to correct it.
1. Partially drain the pool
Partially draining your pool is probably the best choice since you should be doing it occasionally anyway.
>>Read: How to drain an above ground pool
It will give your pool sort of a refresher and allow you start with some cleaner water.
You don’t need to drain it completely and it will be up to you as to how much you start out with.
For example, you might choose to start by draining 1/4th of the water and then refilling it; you’ll then need to test the chlorine again to see if that corrected the issue.
If not, you’ll need to repeat the process until your total chlorine and free chlorine come out equal.
2. Non-chlorine shock
Non-chlorine shock oxidizes the water, restoring the balance and making it cleaner. To determine how much shock to add, you will use this formula:
(Total Chlorine – Free Chlorine) x (#of gallons/10,000) x 2 = amount of shock to add
After adding the shock to the pool, wait a few hours and test again. Repeat the process if necessary.
3. Chlorine shock
In order to break chlorine lock with shock, breakpoint chlorination needs to be achieved.
This is where large amounts of chlorine is added in order to break up the chemical bond of the chloramines. And chlorine shock is the best product to use for this method.
To perform this, you first need to make sure your pH is balanced at 7.2-7.6.
There are formulas available to determine how much chlorine is needed in order to reach breakpoint chlorination, but it seems to work just as well if you follow the directions as you would if you were normally shocking your pool.
Then wait a few hours and test the chlorine levels again.
If it doesn’t work, either continue adding pool shock or use one of the other methods we suggest.
Chlorine lock sometimes does take a little work to break, but it’s extremely important to keep your pool safe and clean for swimming.
If your pool has chlorine lock, no amount of chemicals will be able to kill off the algae or bacteria lurking under the water, so pay attention to the signs and correct the issue immediately.
If you seem to be experiencing this problem repeatedly, consider lowering the amount of CYA you use when you chlorinate.
Keep your pool happy and clean and your swimmers will stay that way as well!
Hi, I’m Matt Harper, the founder of poolcareguy.com, a site I started with one simple mission: to help people around the world clean and take care of their pools and hot tubs on their own, without the hassle.
I’m not a professional pool cleaner and don’t have any formal training, I’m just an average guy who loves hanging out by his pool and hot tub and taking care of it. After many years on the job, I’ve become quite good at it.
On this website I will be teaching you absolutely everything I know about pools and hot tubs.