Free Chlorine vs. Total Chlorine

Chlorine is a natural chemical element that is capable of disinfecting water. It has a wide variety of purposes that range from keeping water clean to providing clean drinking water to killing bacteria and other microorganisms in swimming pools. Although chlorine is mainly used as a disinfectant, it is also used to make paints, medicine, and textiles; chlorine is a necessary element in producing PVC (polyvinyl chloride), which is a kind of plastic that is used in pipes, vinyl flooring, and films.

But the main focus of this article is chlorine used for cleaning and disinfecting purposes. When you add chlorine to the water, it breaks down into more minor elements like hypochlorous acid and hypochlorite ion that kill the unsafe microbes in the water. If organic nitrogen or ammonia is also present in the water system, chloramines (chemical compounds that contain nitrogen and chlorine) form–chloramines are also known as combined chlorine.

Free chlorine, measured in parts per million (ppm), refers to the volume of chlorine that is “free” or available to kill and eliminate harmful microorganisms and sanitize contaminants. Free chlorine is yet to bind itself to microorganisms and pollutants in chlorinated water. Combined chlorine develops when free chlorine binds itself to pollutants in the water system, i.e., while your water system is being sanitized. Total chlorine is the total of free chlorine and combined chlorine.

Free Chlorine vs Total Chlorine
 Free ChlorineTotal Chlorine
ValueThe value of free chlorine is the amount of chlorine available to disinfect water and kill dangerous microbes present in the water.The total chlorine value should be equal to or, at the very least, a bit higher than free chlorine. For example, if your pool is clean, the value of combined chlorine would be zero, so free and total chlorine would be equal. But if your pool is dirty, the value of combined chlorine could be anywhere from 0.2 to 0.5 ppm. In such cases, the total chlorine value would be higher than free chlorine.
FormulaThere is no formula for testing the amount of free chlorine in water; you can use testing methods such as test strips, test kits, or a digital chlorine sensor (this is the most accurate means of testing for chlorine). You can also take a sample of your water to your local pool store to be analyzed by professionals.The formula for calculating the amount of total chlorine in water is free chlorine added to combined chlorine: total chlorine (T) = F + C (free chlorine + combined chlorine).
DefinitionFree chlorine is the quantity of chlorine that is “free” to inactivate harmful microorganisms and contaminants to keep the water clean.Total chlorine is the total of free chlorine and combined chlorine.

Differences Between Free Chlorine and Total Chlorine

The key difference between free chlorine and total chlorine lies in their definitions and components.

Definition and Defining Elements

Free chlorine is the chlorine available to disinfect your pool, while total chlorine is the totality of free chlorine and combined chlorine in the water. Free chlorine is made up of unreacted hypochlorous acid and hypochlorite ion. When you add chlorine to the water, it dissolves into hypochlorous acid, further dissociating and combining with oxygen to form a hypochlorite ion.

Components

Free chlorine is the amount of chlorine available to disinfect and sanitize water. On the other hand, total chlorine is the amount of chlorine available and unavailable to disinfect water.

Similarities Between Free Chlorine and Total Chlorine

Chlorine Levels

The chlorine levels in water systems such as swimming pools or hot tubs determine how effective the chlorine treatment would be. Chlorine levels must be neither too high nor too low. The ideal range for free chlorine in pools is 2.0 to 4.0 ppm, but swimmers may also be safe if the chlorine levels are as low as 1.0 ppm and as high as 5.0 ppm. As much as possible, the total chlorine levels should be equal to the free chlorine levels – if total chlorine levels are higher than free chlorine, there are pollutants in the water.

Can be Used to Measure Combined Chlorine

In the absence of an accurate test for combined chlorine, you can use the levels of free chlorine and total chlorine to determine the combined chlorine levels in the water. Ideally, combined chlorine should hardly be detectable in water, and it should be no more than 0.5 ppm. High levels of combined chlorine mean that free chlorine is currently breaking down the contaminants in the water, but your free chlorine level is not enough to do the job.

In the absence of a test for combined chlorine, you can measure the water’s free and total chlorine levels and if total chlorine levels are higher than free chlorine, subtract free chlorine from total chlorine to get your combined chlorine.

Can be Tested/Detected

Both free and total chlorine can be tested in various ways, including by way of digital chlorine testers, test kits, or test strips. Chlorine test kits are available in different types. Still, they all have similar functionality: add a few drops of some reagent to a sample of the water, and the water will change color–you can compare the color to the color panel available on the instruction sheet of the test strip. Chlorine test strips come with chemical pads that change color to estimate the amount of combined chlorine, free chlorine, and total chlorine in the tested water.

Conclusion

Chlorine is commonly used to disinfect water, e.g., drinking water, swimming pools, hot tubs, etc. Chlorine is also a common compound in bleaching agents; this is a testament to its disinfecting qualities. Free chlorine and total chlorine are different types of chlorine used to detect how clean water is and improve water quality with information on the levels of free and total chlorine.

The main difference between total chlorine and free chlorine is that total chlorine, the total amount of free chlorine and combined chlorine, is the amount of chlorine that is available and unavailable to disinfect water and free chlorine is the amount of chlorine available to sterilize water.

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