Chemical in Focus: Pool Chlorine

After years of dealing with pool chlorine, I’ve come across a realization that I’ve never actually focused on what chlorine was. Yes, we know that it’s needed, but how does it actually work? Well, let’s answer that question today in a way that doesn’t need a PHD and doesn’t need a giant stack of scientific journals to know what we’re talking about.

Pool Maintenance: More science than Art

Some people will say that they know exactly what chemicals to add to their pool just by looking at the pool. These are the types of pool owners that consider pool maintenance as an art. Here at Mr Pool Man, we recognize that pool care is a science, it’s a very precise science that is really unforgiving and doesn’t leave room for interpretation or “gut feels” especially when it comes to sanitising the pool.

What exactly is pool chlorine?

In a nutshell, pool chlorine is the chemical that’s responsible for sanitising our pool. It kills off any organic contaminants in our pool that can cause anything from algae blooms to health-related problems like ear infections and some forms of fungal infections. In a perfect world, we would love to check and balance our chlorine levels every day but that’s just not doable so at the very minimum, check and balance your chlorine levels twice or three times a week to make sure that our pool water remains sanitised.

How exactly does pool chlorine work?

I could go on and rattle on about how chlorine works on a molecular level but I decided to keep it simple and easy to understand, after all, we're all here for relaxation. If we wanted to become masters in chemical reactions, we would have gone back to Uni right?

Chlorine works by binding/exchanging atoms with organic contaminants, causing them to break down and change shape. And since these are simple organisms, once they change shape, they cannot function properly and they die. Simple and easy. For more information about how do Pool Chlorinators work, check this article by clicking here.

Free Chlorine? Combined Chlorine? Total Chlorine?

Aren’t these all just the same thing? This is one of the things that many swimming pool newbies get confused with. If they see chlorine, they’ll just assume “Oh, it still has chlorine, it’s fine” when it actually isn’t.

  • Free Chlorine - This is the most important number that we should be looking at when we’re talking about sanitising our pool. The “Free” means that this chlorine is still free to do its job of killing all the baddies in your pool. For optimal pool santising aim for a free chlorine level of 1 PPM to 3 PPM.
  • Combined Chlorine - These are the chlorine particles in your pool that have been used up or have combined with organic materials and are basically just waiting to be oxidised. They’re still detected as chlorine, but they’re no longer actively sanitising the pool and it’s not a good indicator of sanitising power.
  • Total Chlorine - This indicator is basically the sum of your Free Chlorine and Combined Chlorine. This number should be as close as possible to your free chlorine for maximum sanitising power. If this number is markedly higher than your free chlorine then you might have a problem on your hands with a chlorine lock, more on that later.


Note: If you notice your total chlorine levels slowly rising, you may need to add more chlorine to your pool or even shock your pool to get rid of the excess combined chlorine.

The Strong Chlorine Smell in Pools

Many people who don’t have much experience in maintaining a pool will probably think that having a strong chlorine smell in pools is a sign that there’s a lot of chlorine. This is partly true, there is a lot of chlorine in the pool, but not the good kind. A strong chlorine smell is a sign that chloramines or combined chlorine levels are higher than your free chlorine level (which doesn’t smell like anything) and the sanitising power of chlorine in the pool has been compromised. The cure for this is actually adding more chlorine and reaching break even chlorination. For more information, you can check out Mr Pool Man’s guide to break even or breakpoint chlorination here.

Shocking your pool with chlorine

A term that is being thrown around when it comes to pool maintenance is “shocking”. It has nothing to do with electricity but it simply means that you’ll be adding chlorine in amounts that are usually higher than what you add for maintenance. There are many types of pool shock available so we recommend checking the instructions on the packaging for application instructions. We say this because while the dosages are different, the situations that call for shocking your pool are the same. So when do we shock our pool?

  • To get rid of combined chlorine or chloramines. As a rule of thumb, if your combined chlorine is 0.5 or higher, shock your pool before it becomes a chlorine lock.
  • To quickly raise the free chlorine levels in your pool
  • To quickly kill off algae or to treat green water
  • After flooding or heavy rain
  • After a heavy pool party
  • After continuous sunny days (yay Australia!)

For more information on shocking your pool, see Mr Pool Man’s guide on how to shock a pool here.

Chlorine and UV (sunlight)

Chlorine doesn’t like sunlight. The UV rays burn up chlorine so the best time to apply chlorine would be late in the afternoon or early in the evening and when there are no more bathers in the pool. Cyanuric acid is usually added to pools to protect the chlorine from the UV rays so that they stay in your pool longer and provide sanitising power longer. We won’t go that deep into cyanuric acid because this post is dedicated to chlorine, but if you’re interested in learning more about cyanuric acid or stabilizers, check out this post: Is Stabiliser a Friend or Foe?

General Chlorine Handling Guidelines

Of all the pool chemicals, chlorine will be the one that you will be handling most of the time so it’s helpful to keep these chlorine handling guidelines in mind so that you’ll be safe whenever you handle chlorine.

  • Never add water to chlorine, always add chlorine to water to prevent accidents
  • When adding granulated or liquid chlorine to your pool, always broadcast it around the pool and never in one spot.
  • Never pour chlorine directly into your skimmer box.
  • Never mix different kinds of chlorine
  • Never swim in a pool directly after shocking it
  • Never store different types of chlorine near each other
  • Always wear protective gear (gloves and eye protection at the very least) when handling chlorine
  • The hotter the days, the more often you’ll have to dose the pool with chlorine

Salt Water Chlorinators

Now that you know more about chlorine and what it does for our pools it may sound like it is too much of a hassle to monitor and balance. Well, that’s just a fact of pool maintenance that we have to live with. Or do we have to? Salt water chlorinators actually take care of that problem for us. With a salt water chlorinator like the Water TechniX Atomic Salt water chlorinator, you no longer have to test and dose your pool on a daily basis, the chlorinator does that for you automatically! Using salt dissolved in your pool, a chlorinator will break down that salt and turn it into chlorine gas that will sanitise your pool water. No more handling of chlorine on a daily or weekly basis.


Yes, maintaining chlorine levels in a pool may seem like a huge task, dealing with the consequences when not maintaining chlorine levels is even bigger! Think about all of the things you’ll have to do when dealing with green pool water or algae blooms that are caused by inadequate pool chlorination or health conditions that may be caused by bacteria or fungi laden pools right? Still, there’s always the option of getting a salt water chlorinator to minimize our chlorine handling tasks.

Worried about all of the things people say about salt water chlorination? Check out our post on Salt Water Chlorination Myths and Facts so that you can make a better decision on when it comes to chlorinating your pool.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

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