The Difference Between Free Chlorine and Total Chlorine

By Shiloh McGinley

September 29, 2022


Free Chlorine vs Total Chlorine

Free Chlorine vs Total Chlorine

Chlorine is often the chemical that makes people uncomfortable about swimming pools. Well, chemicals, in general, tend to make anyone uncomfortable, especially if it’s going into a place where one intends on swimming around for hours on end.

The truth is, chlorine in the right amount is not only safe, but it’s also necessary to ensure your pool is algae and bacteria-free. Without the proper maintenance of chemistry in your pool, you’ll find the conditions can be worse than if you used no chemicals at all. 

That being said, many people are unaware of how to regulate their chlorine levels properly. They are also confused about the differences between the two most important types of chlorine: free chlorine and total chlorine.

If you’re a novice pool owner looking to be in the know, read all you need to know in the article below:

What is chlorine? How does it work?

chlorine

Chlorine is a chemical that’s used in a wide variety of fields. Having powerful disinfecting and bleaching properties, chlorine is often used as an active ingredient in many cleaning products. 

For your pool, chlorine plays an essential role in killing harmful bacteria and eliminating the growth of different forms of algae. 

Chlorine is used as one of the safer ways to sanitize your pools. When chlorine is added to the water, it forms something that’s called hypochlorous acid which is effective in killing microbes. 

Over time, free chlorine tends to bond with organic materials, such as debris, sunscreen, or natural body oils. This, in turn, produces chloramines. Also known as combined chlorine, chloramine tends to leave the pool through a process of off-gassing — essentially evaporating into the air. 

Too much chloramine though produces that chlorine smell that swimmers dislike. This is likely due to an imbalance in the chemistry of the water.

FREE CHLORINE VS TOTAL CHLORINE

- Free Chlorine 

Free chlorine is essentially chlorine that’s still floating in the water in pure form. It has yet to bind and neutralize any contaminants so, in that sense, you can sort of think about this type of chlorine as chlorine that’s still on guard. 

Free chlorine is the type of chlorine that’s actively searching and destroying microbes. Keeping the free chlorine level optimal is essential if you intend to sanitize your pool. You want to make sure there’s enough free chlorine available to deal with any bacteria and algae that are building up. 

When using a pool testing kit, the most optimal reading you can get for free chlorine is 2-4 PPM (parts per million). 

Too much free chlorine can result in an unpleasant smell. It can also cause irritation to the skin, dryness to the hair, and redness in the eyes. 

Combined Chlorine 

On a separate but relevant note, let’s talk about combined chlorine. Whereas free chlorine is chlorine that has yet to bond with contaminants or organic material, combined chlorine is chlorine that has already bonded with something. 

You can think of it as chlorine that’s already doing its job. 

When testing combined chlorine, you would want levels around 0.5 PPM. or less. If it reads higher than that, then you probably need to shock your pool. High amounts of combined chlorine produce the chlorine smell that many swimmers hate.

Now that you’re up-to-speed on the difference between free and combined chlorine, we can now tackle the meaning of total chlorine.

- Total Chlorine 

In the simplest of terms, total chlorine is the sum of combined and free chlorine. 

Knowing the total chlorine levels is useful if you want to know whether you generally have too much chlorine in your pool or not. It’s very easy to test for and many pool testing kits only ever indicate total chlorine levels.

However, if you want to know the exact levels of free chlorine or combined chlorine, a total chlorine test is essentially useless. In most cases, it would be more advisable to test for free or combined chlorine specifically.

How to test chlorine levels

Swimming Pool Chemical Testing

Unlike testing for other chemicals in the pool, such as pH levels and alkalinity, we recommend a more specialized test for chlorine.  

Anyway, In the market, there are several options a pool owner can choose from for testing chlorine levels. 

  • The first and cheapest option is chlorine testing strips. There are chemicals on these strips that, when dipped into the water of the pool, react and produce a specific color. This color is held against a gradient chart for you to know whether or not you’re in the most optimal range. 
  • Another method is a chlorine testing kit. These require you to take a sample of the water in a vial and add in other chemicals. Like the chlorine test strips, a color will form that you can use to gauge the free chlorine, combined chlorine, and total chlorine levels in your pool.
  • For those with more of a budget (I love this method), electronic or digital test kits are available which provide a more precise reading.

If you want to lower your alkalinityraise or lower your PH levels, we'll cover that elsewhere as the testing & process are different. 

Bottom Line

And that was all you needed to know about chlorine and its different forms. With proper care and the right information, you can make the most out of chlorine and have a pool that’s clean and safe for the whole family.

Shiloh McGinley

About the author

Shiloh McGinley has been in and around swimming pools her whole life. She's seen a lot of products come and go, and she wants to share with you the best products that really work!

Shiloh is passionate about helping people stay safe in the water, and she loves educating others on how to choose the right pool products.

When she's not working, Shiloh enjoys spending time with her family and friends, and swimming - of course!

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