02/11/2020 | Environmental | 9 MINUTE READ

Free Chlorine vs Total Chlorine: What’s the Difference?

swimming pool and beach ball chlorine

Chlorine is a standard chemical element that’s oftentimes used to provide people all over the world with clean drinking water. The reason that chlorine is highly effective and important for water quality monitoring is because it’s able to kill bacteria via a chemical reaction. Whether you’re treating your swimming pool or work in a water treatment facility, using the right amount of chlorine can keep the water free from impurities.

When chlorine is added directly to pool water, it breaks down into such chemicals as hypochlorite ion and hypochlorous acid, both of which are effective at killing bacteria and various microorganisms. You should know the difference between free chlorine and total chlorine because each type of chlorine functions differently when in water. If you want to determine the effectiveness of your sanitation efforts, it’s important to properly identify the levels of free chlorine and total chlorine in the water.

Since chlorine is able to kill bacteria and similar microorganisms, its primary applications involve being used as a disinfectant in swimming pools and for the treatment of drinking water. Chlorine can also be used to make consumer products like textiles and paints. The vast majority of pharmaceuticals will use chlorine during the manufacturing of new medicines.

Because of the many applications that chlorine has, it’s important that you understand how chlorine works and the difference between free and total chlorine, both of which are discussed further in the following.

What is Chlorine and Why Should You Care?

spray bottle cleaner

Chlorine is a chemical element that’s used as an ingredient in a wide range of different types of products. Because of the disinfectant and bleaching capabilities of chlorine, it’s used as an ingredient in many cleaning products. Chlorine is also used in the creation of a wide range of basic consumer products, which include everything from paints and papers to textiles. This chemical is necessary in the production of PVC as well, which is a kind of plastic that can be the primary material for water pipes, vinyl flooring, and window frames.

Why is Chlorine Effective?

green bacteria closeup

The reason that chlorine is effective when used for cleaning purposes is because the element is broken down into smaller chemicals like hypochlorite ion and hypochlorous acid, which are able to kill bacteria and microorganisms in the water. When chlorine is combined with such chemicals as ammonia, the bacteria that you’re attempting to get rid of will become oxidized, which makes them harmless. If you have a swimming pool that you want to keep clean, it’s important to understand how chlorine works to ensure that you always use the right amount. This is a strong chemical, which means that your skin can become itchy when you swim in a pool with high amounts of chlorine in it.

Benefits of Chlorine

Chlorine has some notable benefits when compared to other cleaning solutions, the primary of which is that it’s very strong and highly effective at getting rid of contaminants in the water.

  • While some cleaning solutions can have a high cost associated with them, chlorine is relatively inexpensive, which allows it to scale well to your needs.
  • Chlorine is also easy to use and isn’t as harmful as some other cleaning solutions can be.
  • Chlorine offers long-lasting protection against re-contamination, which isn’t always possible with other cleaning solutions.

The only issues with using chlorine for disinfectant purposes include lower effectiveness in murky water as well as a strong odor.

Understanding the 3 Types of Chlorine

swimming pool chlorine

There are three types of chlorine that you should be aware of, which include free chlorine, combined chlorine, and total chlorine. Free chlorine involves the amount of chlorine that’s able to sanitize contaminants, 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.

The formula of chlorine is free chlorine + combined chlorine = total chlorine.

Free Chlorine

  • Free chlorine refers to the amount of chlorine that has yet to combine with chlorinated water to effectively sanitize contaminants, which means that this chlorine is free to get rid of harmful microorganisms in the water of your swimming pool.

This specific type of chlorine is highly important for monitoring purposes because it’s necessary if you want to sanitize your pool. If you don’t have enough free chlorine in the water, you won’t be able to get rid of the bacteria and other contaminants that have built up.

When you’re measuring for the amount of free chlorine in your pool, make sure that the readings are between 2-4 PPM. This form of chlorine is very different from other types of chlorine because is hasn’t been used yet, which makes it available for disinfection purposes. However, it’s also important that you know about the other two types of chlorine to better understand how to maintain proper chemical balance in the water of your swimming pool or at your wastewater treatment facility.

Combined Chlorine

  • Combined chlorine is a type of chlorine that develops while your pool is being sanitized.

During this process, the chlorine will bind to any contaminants in the water, which creates combined chlorine. When you measure the water in your swimming pool, the amount of combined chlorine in the water should be less than 0.5 PPM. If the numbers are higher, the pool may need to be shocked to get rid of the odor that comes with high amounts of combined chlorine.

Having any combined chlorine in your pool water means that the free chlorine is currently breaking down some contaminants in the water. A clean and fully disinfected pool will have combined chlorine content of zero. If you keep the right amount of free chlorine in your pool at all times, you should rarely have combined chlorine in the pool water.

Total Chlorine

  • Total chlorine is the sum of combined chlorine and free chlorine, which is useful to measure for a variety of reasons.

True chlorine is very easy to test for in 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 zero.

If, however, there is some combined chlorine in the water alongside free chlorine, the measurement of total chlorine is essentially useless. Since this measurement doesn’t denote the different amounts of free chlorine and combined chlorine, it won’t be able to tell you much. 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 that measure for both free chlorine and total chlorine.

How to Test for Free, Combined, and Total Chlorine In Your Pool

boy in swimming pool bubblesMeasuring the amount of chlorine in your pool is essential if you want to keep your pool water clean and sanitized. Maintaining the proper levels of chlorine in your pool will also allow the water to be clear and sparkling. While it’s recommended that you test your pool water every day, your pool should be fine if you only test the water every other day. Testing the pool water is particularly important if your pool is left uncovered, which exposes it to sunlight, rain, leaves, and wind.

There are three methods that you can use to test for free, combined, and total chlorine in your pool, which include chlorine test strips, chlorine test kits, and an electronic/digital chlorine tester. Chlorine test strips are made from plastic with a chemical pad attached to a stick. The chemical pad can react with the water and will change color in order to provide you with a rough estimate of how much free chlorine, combined chlorine, and total chlorine are in your pool.

When looking specifically at chlorine test kits, they come in many different shapes and sizes with the core similarity being that they all use the same process of titration to test the water for chlorine. When using one of these test kits, you will be tasked with adding a few drops of some type of reagent to a water sample to measure the amount of chlorine in it. The water will change color, which you can compare to the color panel available on your instruction sheet for the test kit. The most accurate method for testing the amount of chlorine in the water is by using an electronic/digital chlorine tester, which provides precise readings without requiring you to compare colors.

Sensorex Products

Here at Sensorex, we offer a wide variety of accurate and durable sensors that you can use to test the chemical composition of your pool water. While test kits may be accurate for some simple applications, it’s highly recommended that you use our FCL Amperometric Free Chlorine Sensor, which can provide you with a direct free chlorine measurement that’s listed in parts per million. The technology within this sensor should always provide you with accurate results that will allow you to determine if your pool is clean or needs to be shocked.

Whether you require a free chlorine sensor to determine the amount of chlorine in your pool water or to make sure that your disinfectant is working properly at a cooling tower, the FCL Amperometric sensor should provide you with what you’re looking for.

Pool Chemical Monitoring Systems

three people diving into water poolThere are a wide variety of pool monitoring systems that you can use to make sure that the water in your pool is clean from impurities. It’s important to monitor the water quality in your pool because the buildup of impurities can lead to the development of harmful algae that can make it unsafe to swim in the pool.

The main systems that you can use to monitor your pool include:

  • Automatic pool chemical monitoring systems
  • Smart pool monitoring devices with wireless functionality
  • DIY monitoring with an electronic meter
  • DIY monitoring with standard pool test kits

Here at Sensorex, we can provide you with the sensors and testing equipment that you need to consistently monitor the quality of your pool water. Contact us today if you need help identifying which products are right for you.

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Posted by Sensorex on February 11, 2020

Sensorex is a global leader in the design and manufacture of quality sensors for water quality and process applications. The company offers more than 2000 sensor packages for pH, ORP, conductivity, dissolved oxygen, free chlorine, chlorine dioxide, UV transmittance and other specialty measurements, as well as a full line of sensor accessories and transmitters. Its expert technical support engineers solve analytical sensor challenges with custom designs and off the shelf products.

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