Difference Between Free Chlorine and Total Chlorine


When you purchase a swimming pool of any size or any type inground or above ground you will learn that chlorine normally is the main chemical that will keep your pool clean, clear, and sanitized free of contaminates but there are different types of chlorine you need to know about that are discussed here. What is the difference between Free Chlorine and Total Chlorine?

Free chlorine involves the amount of chlorine that’s available to sanitize contaminants while total chlorine is the sum of free chlorine & combined chlorine which is a weaker type of disinfectant directly bound with the contaminants. The equation is (Combined chlorine + Free chlorine = Total chlorine)

Having been an inground pool owner myself for many years I have found that keeping things simple is the best way of controlling your swimming pool or else you’ll be running up to the pool center panicked that you won’t have your pool opened by Memorial Day. Understanding this article hopefully will take some of that anxiety away.

What is the Difference Between Free Chlorine and Total Chlorine

 

Free chlorine refers to the amount of chlorine that is readily available to kill any bacteria or other contaminants, as soon as they appear in the water. The optimal levels of free chlorine are between 2 and 4 ppm. Free Chlorine is the best chlorine and needs to be monitored and closely tested daily.

Combined chlorine is a term used to describe free chlorine that has bound itself to a contaminant or organic material, such as skin oil, sweat, or urine. While it is acceptable to have combined chlorine levels below 0.5 ppm, a clean and disinfected pool will have no combined chlorine present.

Having too much combined chlorine can result in a strong chlorine odor, eye redness, and skin irritation. Total chlorine is the sum of free and combined chlorine. It is easy to monitor the total chlorine levels, but this measurement is only useful if there is no combined chlorine present.

First things first, in order to make sure that your pool is clean, disinfected, and safe, it is essential to routinely monitor and maintain the chlorine levels. You can test your pool’s chlorine levels by using test strips, test kits, or an electronic chlorine tester. Test strips are the easiest to use.

If your pool is clean, the combined chlorine value can be assumed to be 0, so the total chlorine amount should be made up of just free chlorine. However, there is no sure way of knowing if your pool is completely clean, without testing the difference between free and combined chlorine levels, as contaminants, such as bacteria and other microorganisms are not visible to the human eye. The presence of algae or a characteristic lingering chlorine smell are both indicators of the excess of combined chlorine.

 

The 3 Types of Chlorine

 

There are 3 types of chlorine that exist in your swimming pool which include

  • free chlorine
  • combined chlorine
  • total chlorine.

 

Free chlorine involves the amount of chlorine that’s able to sanitize contaminants in your pool, while combined chlorine refers to chlorine that has combined directly with the contaminants.

Total chlorine is basically the sum of free chlorine and combined chlorine. All important test parameters for determining the sanitizing productivity of your swimming pool.

Knowing where these tests are in comparison with each other can give you a better handle on the chemistry of pool water and how treatment will be successful or not.

What is Free Chlorine in a Pool Water

 

There are 3 types of chlorine that exist in your swimming pool which include free chlorine, combined chlorine, and total chlorine. Free chlorine involves the amount of chlorine that’s able to sanitize contaminants in your pool, while combined chlorine refers to chlorine that has combined directly with the contaminants. Total chlorine is basically the sum of free chlorine and combined chlorine.

  • Free chlorine is the amount of chlorine, measured in parts per million (ppm), that is available to eliminate harmful microbes and neutralize contaminants.
  • Free Chlorine is not yet bound to microbes, contaminants, or chemicals in the pool water.
  • Monitoring free chlorine is the most important part of swimming pool maintenance in order to avoid harmful contaminant levels and keep control of the pool.

You add chlorine product to pool water to sanitize it. Once in the water, free chlorine forms hypochlorous acid and hypochlorous acid, which are active disinfecting compounds that kill disease-causing microbes. This is what you are aiming for when you add chlorine to your pool water.

When chlorine bonds with these and other organic compounds, such as sunscreen or swimmers’ body fluids, chloramines are formed. Chloramines, also known as combined chlorine, leave the pool through off-gassing.

A buildup of chloramines causes the “chlorine smell” that swimmers in the water find irritating. This sour smell may be an indication of poor water quality. Regularly testing for free, combined, and total chlorine levels will help to prevent or reveal water quality issues before problems arise.

  • Free chlorine: ideal range 2.0 to 4.0 ppm, safe range 1.0 to 6.0 ppm

 

Once the Free Chlorine is used up as it starts to react or oxidize with contaminants like nitrogen & ammonia in the water it becomes Combined Chlorine a weaker version of Chlorine.

 

What Is Combined Chlorine in a Pool

 

Combined chlorine develops when free chlorine binds to contaminants during sanitization. When combined chlorine is present in the pool water it indicates that contaminants are present which is pretty important information you need to analyze the health of your pool.

A good working sanitized pool contains zero combined chlorine. Maintaining the proper level of free chlorine in the pool water greatly reduces the likelihood of detecting measurable combined chlorine levels.

  • Combined chlorine: ideally less than 0.2 ppm, safe below 0.5 ppm

 

 

What is Combined Chlorine?

Combined Chlorine is the portion of chlorine in the water that has reacted and combined with ammonia, such as nitrogen-containing contaminants, and other organics that come from a swimmer’s perspiration, urine …………………………..read more

Free Chlorine + Combined Chlorine = Total Chlorine

 

The sum of combined chlorine and free chlorine is total chlorine (combined chlorine + free chlorine = total chlorine). Inexpensive chlorine testing will only show the total chlorine. Since clean chlorinated water contains no combined chlorine, total chlorine in a sanitized pool is the same as free chlorine.

True chlorine is easy to test for in pool water when compared to free chlorine or combined chlorine, which is why many of the more inexpensive chlorine measurement tests will specifically test for total chlorine. In clean water, the amount of total chlorine can be used to determine the amount of free chlorine in the water since combined chlorine should be at 0 ppm.

The measurement of total chlorine residual is really useless because the measurement doesn’t denote the different amounts of free chlorine and combined chlorine, it won’t be able to tell you much about how healthy your pool is.

Even though it can be more affordable to measure for total chlorine, it’s not nearly as effective, which is why you should heavily consider obtaining sensors or a test kit that measures both free chlorine and total chlorine.

However, without a separate measurement of free chlorine, it is impossible to confirm the absence of combined chlorine. For this reason, it is very important to monitor both total chlorine and free chlorine. You can then subtract the free chlorine measurement from the total chlorine to confirm the level of combined chlorine (total chlorine – free Chlorine = combined chlorine).

  • Total chlorine: should be equal to free chlorine most of the time

 

Free Combined and Total Chlorine Work the Same in a Saltwater Pool

 

4 Ways to Reduce Chlorine Levels in Your Swimming Pool
  1. Stop Adding Chlorine. The simplest step to bring down chlorine levels is to stop adding chlorine to the pool. …
  2. Remove the Pool Cover. …
  3. Use Chemical Agents to Reduce Chlorine Levels. …
  4. Drain Some Water and Refill the Pool. …
  5. Keep Testing.

 

 

Conclusion:

Free chlorine vs total chlorine in a saltwater pool works the same as in a freshwater pool. It involves the amount of chlorine that’s able to sanitize contaminants, while combined chlorine refers to chlorine that has been combined directly with the contaminants. Total chlorine is basically the sum of free chlorine and combined chlorine.

Free chlorine involves the amount of chlorine that’s available to sanitize contaminants while total chlorine is the sum of free chlorine & combined chlorine which is a weaker type of disinfectant directly bound with the contaminants.

The equation is (Combined chlorine + Free chlorine = Total chlorine)

 

 

What happens if Total Chlorine is Higher than Free Chlorine

Free Chlorine (FC) reacts with pool H2O first as Hypochlorous acid 60 to 100 x’s more effective at oxidizing microorganisms than the next stage hypochlorite ion which combines with ammonia making chloramines tested as Combined Chlorine (CC) …………………………………………………………………………read more

 

 

JimGalloway Author/Editor

 

References: 

MyWaterEarth&Sky What is Combined Chlorine

Feature Image Combined Chlorine by Poolonomics.com

 

 

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