Last Updated: December 6, 2020

How to Break Chlorine Lock in Pool

Written By: Pool Care Guide

Some say that chlorine lock doesn’t exist and others argue that it does. It’s semantics. The point is that your chlorine is less effective because it is too busy making bonds with molecules that aren’t part of the bacteria or algae that are attacking your pool. 

Let’s discuss a few of those so that you can understand what we are trying to accomplish. After we tell you how to fix your “Chlorine Lock” problem, we get a bit more in-depth and answer some common questions. In the end, our view is that it doesn’t really matter whether you call it chlorine lock or not. The important thing is to have an implementable solution, and we have a few of those for you.

What is “Chlorine Lock?”

Chlorine lock is essentially your chlorine giving you the busy signal. It can’t deal with your pool’s contaminants because it is already bonding with other molecules. Sometimes it will bond with nitrogen, other times algae, and it can even bond with the hydrogen in your pool if the pH is too low. Very commonly, the chlorine is locked up because the Cyanuric Acid (stabilizer) level is too high. This stabilizes the chlorine to the point that it becomes mostly useless.

How Can You Tell If You Have Chlorine Lock?

The best way to test for chlorine lock is to use a pool chemical testing strip. Test for the following chemicals:

  • Free Chlorine
  • Combined Chlorine (Total Chlorine - Free Chlorine)
  • Total Chlorine
  • Cyanuric Acid (Stabilizer)
  • pH (Hydrogen)

You need to note the Total Chlorine, Free Chlorine, and the PPM of your pool stabilizer. You want the ratio of free chlorine to combined chlorine to be at a 1:1 to a 1:3 ratio, and the cyanuric acid should be between 40 to 80 Parts Per Million (PPM). If you need some help with cyanuric acid, we do have a guide on how to add cyanuric acid to your pool. The instructions and charts make everything very simple.

Free Chlorine

This is the chlorine without any bonds that is ready to conquer and destroy anything that is contaminating your pool. 

Combined Chlorine 

(Total Chlorine - Free Chlorine = Combined Chlorine)

Chlorine that has bonded with a conditioner, urine, bacteria, or some other molecule that is tied up and useless. Conditioners are typically cyanuric acid, and they are also sometimes called stabilizers.

Total Chlorine

We’re sure you probably already get this one. Total chlorine is the sum of the free chlorine and the combined chlorine.

Chlorine Smell

While this isn’t a scientific approach, it can be a strong indicator that your chlorine levels could use some attention. It is counterintuitive, but a strong smell of chlorine is a sign that you need more chlorine rather than less.

The strong smell of chlorine is actually the smell of chloramines. Chloramines are the result of chlorine and a contaminant such as the nitrogen in urine bonding. Adding chlorine or some other form of pool shock should reduce that smell.

Unbalanced pH

Hydrogen atoms are as basic as molecules get. There is very little to them, and they are ready to bond with pretty much anything. Acids are chemicals with an excess of hydrogens. When your pool is acidic, it means that the pH is low and there are a lot of hydrogens. When there are a lot of hydrogens, they start bonding with the Chlorine that is in the pool. 

Depending on which pool expert you listen to - this causes a chlorine lock, or you could say that it decreases the effectiveness of the chlorine. It doesn’t matter how you describe it. It makes chlorine less likely to hook up with pool contaminants because it is already getting handsy with the hydrogen.

Don’t Confuse Calcium Hardness with Chlorine Lock

If your pool looks cloudy and the chemicals listed in the bulleted list above are correct, you might simply have calcium levels that are a bit too high. When there is too much calcium, the calcium can coat the surfaces of the walls and filters. This can cause cloudiness to the water that might make you think that chlorine isn’t doing its job.

Method 1: Drain the Pool If the Cyanuric Acid Is Over 80 PPM

For some pool issues, the only solution is to drain the water. Too much cyanuric acid is one of those issues. It doesn’t evaporate like chlorine or H2O. When it’s in there, it is in there until you drain it.

Draining the whole pool should not be necessary. While cyanuric acid is heavier than water, it is equally diffused throughout the water. Draining a ¼ of the water will approximately drain ¼ of the cyanuric acid. Refill the drained portion of the pool with fresh water, and that will lower the cyanuric acid PPM.

Method 2: Perform a Chlorine Shock If the Pool Has Been Overtaken by a Contamination

We don’t want to go too in-depth because we have already written a guide on how to shock a pool. However, we do want to give a brief explanation. 

When you perform a pool shock, you are adding a relatively large amount of chlorine into the pool. During this time, you should stay out of the pool. You should also only add the chlorine at dusk or night.

The reason you want to wait till night is that any direct sunlight will very rapidly evaporate any chlorine that is in the pool. It seriously only takes minutes before most of the chlorine is gone. That’s why stabilizers are so important to maintain the normal amount of chlorine. It protects the chlorine levels from the sun.

As we said, this is only a brief explanation. If you are going to perform a pool shock, you should click over to the guide.

Method 3: Perform a Non-Chlorine Shock if You Want to Avoid Chlorine

A non-chlorine shock isn’t going to be as effective as chlorine, so we don’t recommend it. We understand that direct contact with chlorine isn’t exactly healthy. However, it also shouldn’t be a problem if you don’t go swimming during the very brief time that the chlorine levels are excessive. 

Beyond that, we don’t have anything useful to add here. The steps to shock a pool are going to be mostly the same whether it is a chlorine shock or a non-chlorine shock.

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