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Free vs. Total Chlorine: What’s The Difference?

Ready for a refresher on pool science? Chlorine is your best friend in the fight against germs and viruses. It’s also a great defense against algae and other biological growth. But do you feel confident about the difference in free vs. total chlorine and why they matter? Let us break down these two important measurements for your water quality.

A Chemistry Lesson

When we talk about pool chlorine, we’re actually talking about different states of chlorine activation. That’s because chlorine undergoes a chemical reaction as it works to destroy contaminants. Basically, its molecular bonds change as it sanitizes. Chlorine takes these four forms in your water:

  • Free Chlorine – The amount of chlorine that is available to sanitize your water; often abbreviated as FAC for free available chlorine.
  • Combined Chlorine – When free chlorine particles bond with containments through oxidation. This is when chlorine is actively working to destroy germs.
  • Chloramines – A chemical that is formed when free chlorine attaches to body waste, personal care products, ammonia, and nitrogen. It often creates a gas that most people think is the smell of a chlorinated pool but is actually a sign that water quality is low.
  • Total Chlorine – This is the sum of both combined and free chlorine.

So why are these measurements important? Chlorine’s sanitizing power is lost if you don’t have the correct amount of free and total chlorine. For example, let’s say you have 3 ppm for total chlorine and 0 ppm for free chlorine. Don’t think that the total chlorine level means your water is clean! Zero free chlorine means exactly that – there’s no available chlorine actively working.

The Right Chlorine Ratio

The reason you need to test your water quality so often is that your chemicals are always hard at work. That means they need to be replenished as they do their job. Chlorine is no exception.

The ideal concentration for free chlorine is at least 1 ppm with a pH within a 7.2–7.8 range, according to the CDC. Chlorine and pH go hand in hand. A higher pH decreases chlorine’s ability to disinfect while a lower pH can lead to eye and skin irritation. It’s like the story of Goldilocks and the Three Bears – you want free chlorine and pH just right!

Test free chlorine concentration and pH at least once per week. You may need to do it more often if you have a heavy bather load, like an all-day pool party. When in doubt, use your senses. If the water doesn’t look or smell quite right, test it.

As a general rule of thumb, add chlorine shock when you have a large weekly bather load. Add oxidizer when your free chlorine is low.

Have more questions about free vs. total chlorine? Check out this video for additional expert insights!

Still have questions? Stop in the store and bring us a water sample or contact us. We have everything you need to stay soaking up the summer FUN!

Article sources
  1. https://www.cdc.gov/healthywater/swimming/aquatics-professionals/chloramines.html
  2. https://www.cdc.gov/healthywater/swimming/swimmers/rwi/chemical-irritants.html
  3. https://chlorine.americanchemistry.com/Chlorine/Pool-Treatment-101/