Taking care of your pool doesn’t have to be a chore… or a chemistry experiment. The chlorine levels in your pool are something you should measure and keep track of on an ongoing basis. This simple task will ensure that your pool stays clean, disinfected, and sparkling all year long.

It is, however, important to know what you’re measuring for and why. Today we’re going to look at the 3 types of chlorine out there and what they can tell you about the cleanliness of your pool.

Wait— what do you mean there’s more than one type of chlorine?

Hold on, take a deep breath, relax. We’re going to take this step-by-step. You don’t need to be a trained chemist to take care of your pool, we promise. Ready to dive in?

What is Chlorine Really and Why Should You Care?

Chlorine kills bacteria through a simple chemical reaction. When you pour chlorine solution into your pool, it breaks down into many different chemicals, including hypochlorous acid (HOCl) and hypochlorite ion (OCl-). 

Both of these chemicals kill microorganisms and bacteria, then combine with other chemicals (like ammonia), rendering them oxidized and harmless.

Chlorine can have some unpleasant side effects, however. It is a very strong chemical with a very strong odor that can sometimes cause swimmers to have itchy skin after a dip or to notice some serious color fading on their brand-new bikini. Ugh, what a bummer.  

Types of Chlorine, Demystified

You may have heard terms like “free chlorine” or “combined chlorine” when you’ve talked to pool specialists at the store and may not have known what on earth they were talking about. Let’s clear that up, shall we?

  • Free Available Chlorine (FAC): This type of chlorine is what you test for in your pool. Free chlorine unused and available, like invisible magic dust floating around, just waiting to sanitize your pool water.
  • Combined Available Chlorine (CAC): This is the used-up chlorine that has already done its job disinfecting your pool. It’s tired, overworked, and spent — but it still matters… and is still lurking in your pool. Waiting.
  • Total Chlorine (TC): This is just the sum of the other two chlorines: free + combined = total.

Easy, right? Now that we’ve gotten the definitions down, let’s talk about why these terms matter and how to test for them in your glorious backyard oasis. 

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

Testing pool chlorine is an important part of keeping the pool water sanitized and clean, and for the health and safety the lucky people you invite to pool parties. Testing your chlorine regularly and adding more when needed helps to minimize bacteria growth in your pool. 

In addition to keeping your friends and family safe from pesky microorganisms, having clean, clear, and sparkling pool water is an added benefit to a properly maintained chlorine level in pools. Because who wants to step into a murky, cloudy pool where you can’t even see the bottom?

Ideally, you should be testing every day, but you can get away with every other day if need be. Frequent testing is especially important if your pool is uncovered and exposed to rain, wind, leaves, grass clippings, and sunlight. 

Testing Methods

There are the 2 main ways to test the chlorine in your pool:

  • Chlorine Test Strips: These are usually made of plastic with chemical pads adhered to the sticks. The chemical pads are designed to react with water and change color to give a good estimate of the chlorine levels in your pool.
  • Chlorine Test Kits: Chlorine test kits come in all shapes and sizes but all rely on the same process of titration. Simply add drops of a reagent to measure the amount of chlorine in the sample and compare the color to the instruction sheet.
  • Electronic/Digital Chlorine Tester: These are devices that measure the chlorine levels in your pool without you having to compare colors manually.

Some Quick & Painless Pool Math

Any form of chlorine added to water has the same chemical reaction: It forms HOCl (hypochlorous acid) and OCl- (hypochlorite ion). These two together = free chlorine, which is the active sanitizer and oxidizer that is doing the job of killing bacteria/germs and removing organics from your pool.

However, when free chlorine has done its job and is depleted, the leftover is combined chlorine. Combined chlorine, also called chloramines, are smelly and irritating. They’re the nasty buggers that make your skin itchy and cause your new swimsuit to fade.

Chlorine in the CAC state is pretty ineffective (compared to free chlorine) and high levels of it in your pool are bad news. They generally mean your pool chemistry is out-of-whack and needs some attention… fast.

A simple way to understand the differences between free chlorine, combined chlorine, and total chlorine is with this easy equation that you’ll use after testing your pool water.

FAC + CAC = TC

For example, if your free chlorine (FAC) levels and total chlorine (TC) levels are the same, then there’s no combined (or used chlorine) in your water. Yay! You don’t have to add any chemicals today. Just make sure to check back tomorrow or the next day.

Safe Levels of FAC: According to the American Chemistry Council, the recommended level should be between 2 and 4 ppm (parts per million) and to never let it fall below 1 ppm. I always aim for 3-4 ppm, just to be on the safe side.

Safe Levels of CAC: It’s best to keep the combined available chlorine (CAC) levels in your pool at less than 0.2 ppm. Some health departments in the USA set a maximum level at 0.4 ppm. If your pool exceeds that, the health department can get involved. You might even notice the “pool smell” of chloramines at any level above 0.2 ppm of combined chlorine.

Testing Quick Tip: If your free chlorine is higher than your combined chlorine, your pool is sanitized and in good shape. Frequent testing and monitoring will keep it that way!

Conclusion

As you learn more about pool maintenance, you’ll come to appreciate chlorine’s importance in contributing to safe, clean water—making those visions of swimming in a sparkling, clear pool a reality.

Now that you’re familiar with the terminology, you’re ready to start testing your pool for a gorgeous, clean, and sanitized pool all year long. Now it’s time to get swimming! Grab some friends, a towel, and don’t forget the margaritas.