This Is Why Your Pool Won’t Hold Its Chlorine

Holding a chlorine chart the the test strip next to it while evaluating chlorine , alkalinity and pH balance levels.

If you own a pool or manage one, then you might have noticed that there are times when you would not get a chlorine reading after testing. It can be an annoying time for any pool owner. We understand your need to know why the situation can get that bad. Therefore, we’ve done some research on this topic.

So, this is why your pool won’t hold its chlorine. Most times, when pools don’t hold chlorine, it is because they’ve been exposed to conditions that make them have a high chlorine demand. This is the pool water’s inability to keep an adequate level of chlorine, even though it seems to be balanced and correctly maintained most times.

Bear in mind that there are several other reasons why this may happen, but the one mentioned above is often the most popular. In this article, we will be looking at some of the several reasons why a pool won’t hold chlorine. We would also talk some bits about what you can do to salvage the situation. Read on to find out more.

Some Cause of Chlorine Loss in Swimming Pools

Loss of chlorine can happen for several reasons. If you are experiencing this type of problem, take a look at four common issues that might cause your pool’s chlorine issue. 

1. Excessive Level of Contaminants

This easily classifies as the most common cause of chlorine loss. The primary reason behind this is that your water’s chlorine content generally works to fight off any contaminant in the water. However, while trying to attack contaminants, the strength of the chlorine constantly gets reduced. This means that the more contaminants your pool contains, the easier it will be for the chlorine to get used up.

Of course, that happens naturally in every pool, but when it begins to happen too quickly, then perhaps it is time to check the water. Something as simple as a pile of leaves under the water can suck up the chlorine at the same level that bodily oil can do. The whole point from this illustration is that all contaminants, whether organic or inorganic, have the power to affect your water’s chlorine level. Some of the most common contaminants include rainwater, leaves, branches, twigs, lotion, shampoos, etc. 

2. Excessive Heat 

Another popular cause of chlorine loss in swimming pools is excess heat. It’s common knowledge that excess heat can cause the pool water to evaporate quickly. Even in moments when there’s no sun, you can still see that hot weather has the power to mess with the chlorine level of your pool. Of course, that’s surprising, but it’s true. 

 In moments when solar rays are not messing with your chlorine, the heat from the sun would still stay busy by causing your pool water to evaporate. Of course, every loss of pool water comes with some level of chemical loss. Therefore, after some time, you might notice the chlorine level of your swimming pool drop rapidly. Thankfully, you can easily avoid this by covering your pool. 

3. Direct UV Rays From Sunlight

Yes, we talked about heat, but this one is different. Most experts are aware of the fact that sunlight and chlorine do not get along. They will tell you that the UV rays from the sun have a significant effect on chlorine. 

This is why you are often advised not to allow excessive direct sunlight reflection on your pool. Every exposure to UV rays from the sun would potentially cause chlorine ions to separate, eventually leading to their destruction. 

You know that with every moment that your chlorine burns away comes a continuous decrease in the sanitizer level. This is why you find chlorine stabilizers in the market today. These are chemicals designed to keep chlorine active for a longer time.

Note, however, that despite the availability of chlorine stabilizers, the sun would gradually take its toll on the water’s chlorine levels. Don’t panic yet because you can also prevent this by shielding your pool from the sun.

The higher the Cyanuric acid (CYA) levels are in your pool water, the longer the chlorine will remain in you water during the sunny day. It is recommended that your CYA levels be around 50 to 100 PPM.

Testing for this weekly, is a good idea. Some chlorine tablets automatically add CYA. This causes your stablizer to gradually get stronger during the swimming season.

Backwashing and draining the pool water is the easisest way to lower CYA levels when too much stablizer is in your water.

4. More Swimmers in The Pool Than It’ll Usually Carry

Group of young girls wearing sunglasses floating in inner tubes having some pool fun.

Events like pool parties and shows typically mean that the pool will get large swimmer loads. Scenarios like this can hugely reduce the chlorine levels of your pool. Therefore, the next time your pool test results show lack of chlorine, it could be because of a party you recently had in it. 

The thing is that your pool typically adjusts to a capacity that can carry you and your family. The adjustment of the pool would result in less chlorine loss under normal conditions. However, when you expose the pool to more swimmers, things get different.

With more swimmers come more contaminants. Your chlorine would be left to fight against more than it is used to fighting, forcing it to get used up faster.

How To Raise The Chlorine Level of Your Pool

When the chlorine level of your pool gets low, the only easy solution would be to raise the pool’s chlorine level. Thankfully, this is usually easier than trying to lower the chlorine level. With the following steps, you can get the chlorine level of your pool back up. 

Test the FAC Concentration

Start by testing the FAC (Free Available Chlorine) concentration of the pool. Testing would typically help you to determine how much you’ll have to raise the chlorine level. For cloudy or green waters, you would need to shock the pool by raising the chlorine level to 10 ppm or more.

However, you’ll need to wait for it to drop below 5 PPM before attempting to swim in it. On the other hand, if you are dealing with clear water, then just adding enough to raise the concentration to 1 to 4 ppm would do the job for you.

I like to use the Clorox Test Strips which has an app that helps give precise readings simply by taking a picture of the Clorox Smart Strip with your smartphone, my article explains just how it works.

Calculate the Volume of your Pool. 

Generally, this should be easy for most people, considering that it is a common practice to know this beforehand. Don’t panic if you don’t. Measure the length and width of the pool, as well as its average depth. Multiply these numbers together, then convert whatever result you get into gallons. Typically, one cubic foot is equal to 7½ gallons. 

I have a great artice with an easy to use calculator that will easily caclulate the volume of water in you swimming pool.

Carefully go Through the Instructions.

You’ll find the instructions written on the label of the product. This is the sensible thing to do for every product you want to use. At least, from the instructions, you can easily tell how much of the product you’ll need to add to raise the concentration of the chlorine to the level you desire based on your pool’s overall volume. 

Backwash the filter of the pool. 

Backwash hose that is pouring ditry water out while the pool is being backwashed.

Also, vacuum any sediment you find on the bottom. Doing this will ensure that a significant part of the added chlorine stays available in the pool water for lenthier period of time.

If possible it is always best to vacuum and backwash if you are using a sandfilter prior to adding new chemicals. This allows your pool water to circulate at maximum efficiency while having less contaminents that could reduce the effectiveness of the chlorine.

Add the Required Quantity of Chemicals

It is best that you do this in the early evening since this will help prevent degradation due to direct sunlight. It is also better to pour shock around the edges of your swimming pool.

If you have a pool with multiple water levels, try and pour any shock you add to the water as near the deep end of the pool as well.


In the end, it’s not just about knowing why your pool won’t hold chlorine. It’s about being able to take the right actions to get it back to its best state. In this article, we’ve seen that there are several reasons why your pool may lose chlorine. We’ve also seen some useful steps to getting it back to your desired chlorine level.

If you want to enjoy your swimming experience, then the chlorine level is something to watch out for in your swimming pool. If you test your chlorine levels once per week, you will begin to master the best system that works and keeps optimal chlorine levels.

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