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

Pool Chemistry is something that every pool owner has to deal with. Balancing your pool is a must to obtain those “crystal clear waters”. One of the keys to this pool chemistry is knowing the difference between Free Chlorine and Total Chlorine. Today on Pool Calculator we are going to dive into the difference between the two, and how much Free Chlorine you should have in your pool.

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Free Chlorine

Simply put, Free Chlorine is the amount of chlorine available to sanitize water in your pool or hot tub. Free chlorine is added in order to clean and sanitize your water. This is the value you actually test for. This is important because while you may know the “Total Chlorine” you inject into your pool, all of that chlorine isn’t used. It is important to remember that stabilizers like Cyanuric Acid reduce the sanitizing power of this free chlorine. This means that you always need to test your Cyanuric Acid level when you test for free chlorine. This ensures you know exactly how much chlorine to put into the pool. This combined value if referred to as the Suggested Free Chlorine (SUG) level. Suggested Free Chlorine testing is available in our Pool Calculator Tool.

The optimum level of Free Chlorine in your pool water is between 2 to 4 parts per million. This ensures that your pool will be sanitized and optimum for use, without the irritating effects of too much chlorine.

Combined Chlorine and Total Chlorine

Total Chlorine is the combination of free and combined chlorine that is in your pool. Combined Chlorine is the chlorine that has already been used up by the pool for the sanitization process. This means that when its in the water it is limited in its efficiency. This is where Free Chlorine steps up. FC does the sanitizing when Combined Chlorine is no longer useful. Total Chlorine is important because it is the total amount of chlorine that is actually in your pool water, but is not testable.

It is important to know the differences between these two to make sure your water is clean and clear, but also safe for swimmers.

The Chlorine Equation

When breaking down chlorine, there is a simple equation to calculate Total Chlorine:

Free Chlorine (FC) + Combined Chlorine (CC) = Total Chlorine (TC)

For an introduction on Swimming Pool Chemistry, click here.

Our Testing Recommendation

You can always get a professional to come out and test your water for you. However, doing the test yourself is easy. All you need is a testing strip and our Pool Calculator Tool. You simply dip the testing strip in the water, and plug your output numbers into our tool. The tool will then spit out exactly what you need to add to your pool to make it perfectly balanced. This works with chlorine, as well as many other pool chemicals.

It is easy to treat your water and save a bunch of money when you use Pool Calculator to balance your pool.

Pro tip: Treat your pool or hot tub with chlorine at night. UV rays can cause chlorine compounds to break down faster, limiting the usefulness of the chlorine you inject.

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