Free Chlorine VS Total Chlorine: What Are Their Differences?


Having high levels of chlorine in the swimming pool can be very dangerous. In above normal levels, the chlorine can cause discomfort in swimmers since it can cause irritations and burn the eyes. But when chlorine levels reach the danger zone, it can actually cause serious health problems.

This is why making sure that the pool is regularly tested is very important. When checking the pool’s chlorine levels, most testing kits will show you results of how much free chlorine and total chlorine is in the water. This can actually cause confusion especially to those who can’t interpret them properly.

Chlorine is basically an element that can readily combine with other elements to form chemical compounds. When used in pools, it will slowly combine with the other elements in the water and act on microbes. This results in the formation of free chlorine, and chlorine that has been used for sanitation.

Free Chlorine VS Total Chlorine: What Are Their Differences?

What Are The Three Types Of Chlorine?

chlorine bars

When adding chlorine in the water, it will begin what it was made to do, to start the process of sanitizing the water and removing microorganisms. To do this, chlorine needs to form a chemical bond with the hydrogen and oxygen found in water. This will result in the formation of hypochlorous acid.

As soon as the acid is formed, it will slowly use itself up and attach itself to microorganisms to disinfect the water. This results in the formation of three types of chlorine. The free chlorine, the combined chlorine as well as the total chlorine.

Although these three all comes from the same source, it is very important for pool owners to know what each type of chlorine is. Free chlorine is basically the chlorine that has formed into hypochlorous acid or hypochlorite. This chlorine is ready to be used for disinfection or for sanitation purposes.


Free chlorine is what you will have to measure if you want to make sure that the pool does not have too much chlorine in it or if you want to check if the chlorine levels are still enough to keep the water clean. Combined chlorine on the other hand is the chlorine that has already been used up for disinfection.

Combined chlorine is also what is created when free chlorine combines with ammonia or nitrogen that is found in the pool. You need to keep in mind that aside from being used for disinfection, chlorine can also be used to remove contaminants such as urine and other impurities in the water.

Although combined chlorine can still be found in the water, it will be significantly less potent because it has already done its job. Total chlorine on the other hand, is the total number of chlorine that is present in the water. It is basically the sum of both free chlorine and combined chlorine.

Free Chlorine VS Total Chlorine

chlorine bar

Those types of chlorine are very different from each other. As mentioned, free chlorine is the type of chlorine that is actively seeking microorganisms and contaminants while total chlorine is just the summation of all the chlorine that is present in the water, whether they are free or combined.

When it comes to pool maintenance, you need to make sure that you are able to check the results of both types of chlorine. Make sure that the free chlorine level is between 1- 3 parts per million. This will help keep the pool clean and ensure that the chlorine levels are not too high.

On the other hand, if you are testing for total chlorine, you need to keep in mind that the result will serve as your guide whether you need to add more chlorine or not. For example, if you get similar results for free and total chlorine, it means all of the chlorine in the pool are still active.


chlorine dispenser

So you will understand better the difference between free chlorine VS total chlorine, you need to know how chlorine works. As soon as it gets into contact with water, it will form chlorine-based chemical compounds that are active against contaminants and microorganisms. This is known as free chlorine.

Total chlorine on the other hand will help you determine whether or not you need to add more by giving you the sum of all the chlorine present. Deduct the free chlorine with the total to determine the amount of combined chlorine.

Since combined chlorine also refers to the amount of chlorine that has already been used up because of the presents of contaminants, you will now know how much active chlorine to add so you can make sure that the free chlorine levels will stay between 1 – 3 parts per million.

About the Author Emily Taylor

My name is Emily Taylor, gardening is my passion and I’m looking forward to sharing it with everyone. I know that there are millions of people out there want their backyard and garden be attractive just like their front yard, so I am here to help you create your own backyard paradise.

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