3 Demystified Types of Chlorine: Free, Combined, and Total Chlorine

It is essential for pool owners to know the three types of chlorine. Learn more about free chlorine, combined chlorine, total chlorine, and their differences.

Details matter when it comes to your pool water. Learn more about free chlorine, combined chlorine, total chlorine, and the difference between the three.

3 types of chlorine

It is essential for pool owners to keep chlorine levels under control. This may seem like an easy task, but there are actually three different types of chlorine: free chlorine, total chlorine, and combined chlorine. 

Knowing the difference between these chemicals and which type you’re testing for can help you keep the water in your pool safe for everyone who swims in it.

Let’s begin. 

What Is Chlorine, and Why Should You Be Concerned About It?

Chlorine is a Chemical

Chlorine is a chemical that you put in your pool to keep it clean and free of bacteria. . It also kills algae, so many pool owners choose to add chlorine even if they don’t want to deal with other chemicals (like salt). You may have heard about chlorine gas — this is a different type of chlorine. 

The main concern with using chlorine in pools is not letting it get too high. High levels can irritate the skin, eyes, nose, and throat.

What Makes Chlorine Effective?

Chlorine is effective in killing bacteria because it produces a chemical reaction called oxidation. In water, chlorine reacts with metal ions (which are found in large amounts) and certain organic compounds. 

This causes the iron(III) and manganese(III) to form a non-soluble compound in water. The compound then decomposes into iron(II) or MnO 2.

The chlorine binds to the organic compounds by donating an electron to them and causing them to become oxidized. This reaction follows in the oxidation of the organic compounds, which kills off any bacteria they come into contact with. 

How Is Chlorine Measured?

measuring pool's pH level

Chlorine is measured in three categories: free chlorine, combined chlorine, and total chlorine. Free chlorine is a measurement of the amount of active chlorine that is present in the water. It does not include any other types of chlorine, like gas or combined products (powdered chlorinators or granular products). 

Total chlorine contains all types of chlorine, including free and gas produced. The total chlorine level also adjusts for the amount of acidity in the water. Some pools have a required level set by law, while others use a calculation based on the pH level, which varies with local weather conditions and other factors that change the pH level over time.

Benefits of Chlorine

Chlorine is a much-maligned chemical that has been used to purify water since the seventeenth century. It is now the most widely used disinfectant in water, and it is often necessary for keeping our drinking water and pool safety. Chlorine (commonly called “chlor”) is a liquid chemical built by connecting chlorine gas and sodium chloride molecules together. 

Chlorine’s most important function is its ability to destroy harmful bacteria through oxidation, which leads to the chlorination of organic compounds in water. It can also kill algae with its high reactivity, oxidation of metal ions (essential micronutrients), and decomposition of organic compounds into iron(II) or MnO 2.

What Are the Three Types of Chlorine?

Free Chlorine

The amount of chlorine that is present in the water but not used up as it reacts with organic compounds. 

Combined Chlorine

Combined chlorine includes all types of chlorine, including free and gas produced. Combined Cl is a measurement of the amount of combined chlorine that is present in the water.

Total Chlorine

Total chlorine is the minimum amount of chlorine that is required for the disinfection of a water system. It is used to kill microorganisms in water like bacteria and viruses. 

Total chlorine includes free chlorine (Cl2) as well as combined chlorine (ClO2). It can also be measured as calcium hypochlorite solution or elemental chlorine in parts per million by volume.

Why Is It Important to Check the Free, Combined, and Total Chlorine Levels in Your Pool?

Chlorine is important in many ways. The two fundamental reasons are to kill bacteria and keeping out algae from growing. Chlorine also kills harmful viruses like hepatitis A, even if they have developed resistance to other chemicals like chlorine dioxide or bromine. 

It can also help stop the spread of typhus, bacillary dysentery, cholera, rotavirus enteritis, and cryptosporidiosis in water systems that are disinfected with chlorine.

algae growing in the swimming pool

You should check the levels of free and total chlorine before using your pool so that you don’t risk exposing yourself to any of these illnesses!

It’s also a good idea to test for combined chlorine levels once every four weeks for pools served by a continuous feed system. This is because combined chlorine levels can get too high if there’s not enough water in the pool. 

Combined chlorine levels are also high for the first few hours after you’ve added a granular filter chlorinator to the pool because it takes some time to react with water and dissolve. 

This can cause skin or eye irritation for someone who comes in to swim afterward, so it’s essential to test for this level at this time (especially if you have special circumstances like a lot of people swimming who may be more sensitive).

Acceptable Chlorine Concentrations for Public Health and Safety

You can check your pool’s chlorine levels, preferably by using a pool liquid test kit, as they are more accurate than other methods. You can, however, utilize test strips or a digital or electronic chlorine tester in addition to these methods.

Pool test kits usually test different chemical levels such as pH, chlorine, acid demand, and total alkalinity. Moreover, some pool test kits also cater to testing bromine, total hardness, and cyanuric acid.

It’s advisable to test your pool chemistry at least two to three times a week for chlorine levels and pH levels. Slide the indicator solution (or tablets) into the chlorine level portion of the vials after dropping the combined vials at least 18 to 20 inches below the pool’s surface.

Most testing kits show results in colors. The standard chlorine level for most pools should be between 1 to 3 ppm. Chlorine levels lower than 1 ppm put swimmers in danger of contamination; never allow chlorine levels to go below down this level. 

Chlorine levels higher than 3 parts per million (ppm) will continue to destroy pollutants but may also put you at risk of eye and skin irritation.

What Is the Best Way to Scale up the Chlorine Amount?

To increase chlorine levels in a pool, you can add granular or liquid chlorinators. Granular chlorinator allows for the quick dissolving of the chlorine, while a liquid one requires further dissolving to establish chlorine concentration. 

In addition to adding granular or liquids, you should also consider adding shock treatments. This will help push out contaminants before they become ingrained into the water. It also helps to address and correct pH since it typically decreases when there is an excess of chlorine and bromine and increases when there is an excess of acids like sulphates and phosphates.

What Is the Best Way to Scale Down the Chlorine Amount?

You may either wait it out or replace the existing water with fresh water to reduce the chlorine levels. Allowing your pool some time to return to normal chlorine levels is also a good technique for getting rid of excess chlorination. 

This could be particularly effective on a sunny day because the sun’s UV rays accelerate the breakdown of free chlorine in the water. 

If you want to purge the excess chlorine as quickly as possible, you may always replace part of the pool’s water with fresh, unchlorinated water, which will speed up the process. The new water usually doesn’t have any chlorine but will have some contaminants, which will cause the current free chlorine to be used much quicker.

replacing pool with new water

Measuring chlorine levels in your swimming pool should be a straightforward and quick process that makes sure that your pool is in good and healthy condition. If your combined chlorine levels are lower than your free chlorine levels, you know your pool is in good health and won’t have to worry about anything at all.

Although it may sound complex at first, don’t let free chlorine, combined chlorine, and total chlorine overwhelm you. Once you have further knowledge of what these chlorine types and swimming pool chemistry is all about, you’ll be able to maintain the health of your swimming pool with ease and more confidence. 


Basically, to keep a healthy and clean swimming pool, the most important thing for you to maintain is the chlorine levels in check.

Negligence can cause algae and bacteria to accumulate in your pool that can cause health problems. On the other side, having too many chlorine levels in the pool can cause eye and skin problems. Careful maintenance is needed to keep your swimming pool healthy. Happy swimming!

Check out our website for more information on how to keep your swimming pool healthy. Below are a few of them.

Photo of author

About the author

Brian Anderson

The rather dry pool world out there is in need of some passion to make it shine. With the help of my son Ruben and his wife Maria our mission is to help you create the favorite spot of your house - your pool.

Related Articles...

Leave a Comment