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What is the different between Free Chlorine and Total Chlorine?

You may have noticed when testing your pool water there may be 2 different chlorine readings: Total Chlorine and Free Chlorine. So what is the difference? Chlorine is chlorine, right? Not exactly. The water in your pool has more than 1 type of chlorine, so if you're not monitoring them both, it's possible that your pool may not as clean as you think.

Testing pool water for free chlorine and total chlorine for proper sanitization

Understanding the distinction between total and free chlorine is essential to maintaining the sanitization of your pool for the safety and health of swimmers.

Let's start with the basics:

What Is Free, Total, and Combined Chlorine

Free chlorine

Chlorine dissolves when added to a pool, creating hypochlorous acid (HOCI). This weak acid then mixes with oxygen to create hypochlorite (CIO), an oxidizing ion that is the main component of household bleach. These substances combine to create free chlorine.

This is the chlorine that is free or readily available to kill bacteria and other contaminants in your pool, just as its name implies. When balancing the chemistry of your pool, you test for this. When you add chlorine to your pool it will increase the free chlorine levels. The ideal level of free chlorine in water is 3 parts per million (ppm).

Free chlorine transforms into combined chlorine once it starts to interact with impurities in the water.

Combined Chlorine

Free chlorine oxidizes contaminants such as nitrogen and ammonia to sanitize the water in your pool. During this process, the chlorine that is still available is used up, combines with the impurities it is removing, and then transforms into combined chlorine. 

Even though some chlorine is still present in the water, it no longer has the same sanitizing power as free chlorine.

Total chlorine

This is the total amount of combined and free chlorine in your pool's water.

How to test chlorine levels in swimming pool for safe sanitization

How to know if your pool is safe for swimming?

When testing your pool water, the free chlorine level needs to be higher than the combined chlorine level for your pool to be effectively sanitized. This is why it's crucial to frequently test the water in your pool. If the free chlorine levels are too low, add more chlorine or shock to get the levels up to the ideal range or 3ppm. 

And now you will have a safe and sanitized pool ready for swimming!

Need test strips?

LeisureQuip Pool and Spa 5-way test strips now available to test for free chlorine and total chlorine levels.

LeisureQuip Pool and Hot Tub 5-way chlorine and bromine test strips

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