How Often Should You Add Chlorine to a Pool?

When it comes to maintaining a clean and safe pool, the level of chlorine is one of the first and most important factors to consider. If used too often, it can cause problems for some people. Not often enough, and you probably won’t want to swim in it.

You should add chlorine to a pool as often as needed to maintain free chlorine levels of 2-4 PPM alongside pH levels of 7.2-7.8. This can be measured using test kits as needed. Ultimately, the amount of free chlorine in the pool ultimately determines if more chlorine is needed.

In this article, I’ll cover the common factors that cause more chlorine to be added and explain how chlorine breaks down in your pool. I’ll dive into the specifics about this so that you can best decide exactly what your pool needs.

Factors Increasing the Need for Chlorine in Your Pool

Maintaining a safe swimming environment may seem like a complicated task, but it’s really a matter of keeping track of the chlorine and pH levels.

You can keep track of those levels with a test kit. However, there are some factors leading to lower free chlorine levels that may increase the need for chlorine to be added to your pool.

Start of Swim Season

Depending on where you live, you may not use your pool year-round. If this is the case, you’ll want to make sure you clean it thoroughly before the year’s first use.

It’s also important to shock your pool at this time. This requires treating your pool with an initial high dose of chlorine to bring the levels up.

This is necessary because your pool will be at or near zero chlorination after taking the season off.

Sunlight

Ultraviolet radiation is one of the many factors affecting the chlorine levels in your pool water.

As water is heated, bacteria thrive, forcing free chlorine to go to work. It also evaporates and releases chlorine into the air.

For outdoor pools – particularly those that spend a lot of time uncovered during the day – sunlight will make your free chlorine levels drop faster and require more chlorine treatment.

Frequency of Use

Some pools are used multiple times every day. Others get neglected and host swimmers no more than once or twice a week, even in peak season.

As the number of people – or animals – dropping off sweat and skin cells at your little oasis increases, so too will the amount of chlorine you need to add.

Keep this in mind, especially if you like to host the odd pool party.

Understanding Chlorine Levels in Your Pool

The term chlorine is a little misleading by itself, and testing for overall chlorine levels isn’t all that helpful either.

When first introducing the chemical to a body of water, it interacts with other ingredients and bacteria and begins to change.

As it works to kill bacteria, it becomes less effective, separating into free chlorine and combined chlorine:

Combined Chlorine: This is what chlorine becomes after being used up in killing bacteria. Once the chlorine has reached this stage, it’s essentially useless as far as keeping your pool clean is concerned. Due to this, it shouldn’t be included in the chlorine count.
Free Chlorine: Free chlorine is the term for any useful chlorine still available to kill bacteria. It’s what you want in your pool to fight things like E.coli, hepatitis, and other bacteria. When free chlorine interacts with bacteria, sweat, certain chemicals, or even sunlight, it gradually becomes combined chlorine, making the water less safe.

Chlorine’s Relationship With pH

If all you had to worry about was keeping enough free chlorine in your pool, you might be able to stop reading here, but unfortunately, pH also has to be taken into account.

This is because the effectiveness of free chlorine changes depending on how acidic or basic the water is. As a general rule of thumb, you want the pH to be somewhere from 7.2 – 7.8.

If your pool’s levels are above 7.8, free chlorine will start to become less effective. If it’s below 7.2, the free chlorine will do its job better, but you may end up with other problems like corroded pipes.

You shouldn’t ignore the impacts on the people going for a swim either. The information in the chart below is from the CDC.

pH Levels	Effects
Below 7.2	Eye Irritation Skin irritation pour disinfection
7.2 – 7.8	Most ideal for eye comfort and killing germs
Above 7.8	Eye IrritationSkin irrigation pipe corrosion

Applying This to Your Pool

Test kits are available to measure free chlorine as well as pH.

To carry out these tests, you’ll need to add a solution or powder to a tube of sample water from your pool. You then follow the instructions on the test kit and compare the results to a chart to measure your pool’s chlorine.

The CDC considers a free chlorine count of 2-4 ppm safe for swimmers.

For residential pool owners, I recommend the Taylor K2005 Test Kit (available on Amazon). Not only does this test kit measure free chlorine and pH, but it also contains solutions that track things like calcium hardness and cyanuric acid. It comes with everything you need in a convenient carrying box with the instructions printed inside.

Key Takeaways

The chlorine level in your pool will depend on many factors, but in general, free chlorine should be kept between 2 and 4 ppm and pH between 7.2 and 7.8.

Regular testing is best to ensure this, but at least weigh the factors leading to lower free chlorine levels and adjust accordingly as needed.

For those with high-traffic, high sunlight pools, you’ll likely want to add to the chlorine twice a week. For those with fewer chlorine-reducing factors, once per week should suffice.

Figure out a schedule that works based on your pool’s needs, and enjoy splashing around!