Chlorine: What Is It and How Much Does My Pool Need?

Written By Timothy Te

16th August 2021

Everyone who has a swimming pool is familiar with chlorine, yes we need it to keep our pool sanitised and algae-free, but do we really know what it is? We keep talking about chlorine in a lot of our pool maintenance blog posts but we’ve never really touched upon how it actually works. For a lot of people, that’s actually fine, I mean, we really don’t need to know the nitty-gritty behind how pool chlorine works, the important thing is that we know that it works and we know how much we need to add to our pool at any given time! Right?

How much chlorine does my pool need?

The only correct answer to this question only comes AFTER you test your pool chlorine levels with a test kit like the Water TechniX 7 in 1 Pool Test Strips. The reason for this is that there are a variety of factors that are affecting your pool water’s chlorine levels and we can’t just go “Oh, I’ll add X amount of chlorine every X number of days and that should be good.” By knowing what our current free chlorine levels are, we’ll know exactly how much chlorine we should be adding and eliminating guesswork altogether.

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So how much chlorine does the pool actually need? Ideally, you’re aiming for your pool to have chlorine at around the 1ppm to 3ppm range. Here at Mr Pool Man, we like to keep it around the 2-3ppm range so that there’s time for the pool chlorine to do its job in sanitising the pool before it gets eaten up by the Australian sun.

Are all Chlorine products alike?

In a nutshell, no. Different types of chlorine products all contain different chlorine concentrations. So if you’re switching from one chlorine type to another, all your previous calculations are no longer valid. Don’t worry though, we’ve come up with a helpful list of different chlorine concentrations so you can easily adjust your pool chlorine dosing to match!

To increase the pool by 1PPM per 10,000 Liters

Liquid Bleach - The liquid bleach you see at the supermarkets typically contain a 6% chlorine concentration. To raise the pool chlorine levels by 1PPM per 10,000 liters, you would need to add 162ml by volume of bleach.

Trichlor - Trichlor has 90% available chlorine so a little bit goes a long way! To raise pool chlorine levels by 1PPM per 10,000 liters, you would only need to add 11g of trichlor!

Dichlor - Dichlor has lower available chlorine, around 80% so you would need a bit more (not too much!) to raise your pool chlorine levels by 1PPM per 10,000 liters. You would need to add 18g or 18ml by volume of dichlor to raise 1PPM per 10,000 liters.

Cal-Hypo - Different brands of cal-hypo have different concentrations so it’s a good idea to see exactly what the concentration is before measuring it out and dosing your pool.

  • 48% - You will need 20g by weight or 21ml by volume of cal-hypo 48% to raise your pool chlorine levels by 1PPM per 10,000 liters of water.
  • 56% - You will need 19g by weight or 19ml by volume of cal-hypo 56% to raise your pool chlorine levels by 1PPM per 10,000 liters of water.
  • 65% - You will need 16g by weight or 15ml by volume of cal-hypo 65% to raise your pool chlorine levels by 1PPM per 10,000 liters of water.
  • 75% - You will need 14g by weight or 13ml by volume of cal-hypo 73% to raise your pool chlorine levels by 1PPM per 10,000 liters of water.

 

Lithium-hypo - This is the most expensive type of pool sanitiser out there and for good reason. Lithium-hypo is highly soluble, it won’t raise your pool’s pH levels, it has no calcium, and it is basically your standard chlorine on steroids. Many people shy away from this due to the cost, but if money is no object, this is probably one of the best types of sanitisers to use, especially for those who have chlorine sensitivity. To raise your pool chlorine levels by 1PPm per 10,000 liters, you would need to add 28g by weight or 29ml by volume.

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So what do all of those numbers mean? Simply put, if you have a 40,000 liter pool and you want to raise your free chlorine levels by 2PPM, you would need the following:

Chlorine Type Required X Number of PPM needed X Volume of Pool

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10,000

So let’s say, you’re using the Zodiac Stabilised Pool Chlorine that's available on Mr Pool Man's online pool supply shop which has a concentration of 56% chlorine, and let’s plug in the values needed. (56% needs 19g to raise the chlorine level 1PPM for every 10,000 liters of pool water)

19g x 2 x 40,000 / 10,000

38g x 40,000 / 10,000

1,520,000 / 10,000

= 152g of Zodiac Stabilised Pool Chlorine to raise a 40,000 liter pool’s chlorine levels by 2ppm.

Simply plug in your numbers and you should get exactly how much you need to add to your pool! And the reason why we aim for a number in between 2 and 3 ppm? We acknowledge that tiny measurements aren’t always accurate so a little bit above or below will still lead to chlorine levels that sit comfortable in those safe zones!

This computation also works for shocking the pool! So pool shocking needs about 10PPM or 20PPM so just plug that in to the formula and you’ll know exactly how much chlorine to use to shock your pool! (P.S. You will need UNSTABILISED chlorine to shock your pool and not the recommended product above)

Don’t know what the volume to your pool is? Check your pool’s documentation or measure it yourself with our handy pool measuring guide here.

How to add pool chlorine to your pool

Don’t be tempted to just measure out your pool chlorine and dump it into the pool and be done with it! There’s an actual method to effectively adding your pool chlorine. What you do is that you take a bucket of pool water, dissolve the chlorine in it (especially if you’re using the higher concentration chlorine types) and broadcast it into your pool. This ensures two things:

  • The chlorine is properly dispersed all over your pool
  • You avoid undissolved chlorine from settling on one spot and causing corrosion to your pool surface (remember, chlorine can be quite corrosive!)

If you’re using chlorine in tablet form, be sure to use the appropriate chlorine feeding device and avoid the temptation of popping them into your skimmer baskets. Not only is adding chlorine directly on your skimmer baskets inefficient, but it can cause damage to your pumps and filters as well!

Free Chlorine levels not going up after adding chlorine

This is probably because your pool is overloaded with chloramines and adding small amounts of chlorine is not helping as it is overwhelmed as soon as it is added to the pool. In times like this, you may need to reach Break Even Chlorination or Breakpoint chlorination. This is just a fancy way of saying that you need to shock your swimming pool! For more details on Break Even Chlorination or Breakpoint Chlorination, check out this article here.

Easier Chlorination with a salt water chlorinator

Water TechniX Atomic WTA35 Salt & Mineral Chlorinator - 35g-Chlorinators-Mr Pool Man

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If you value your time or if you just don’t want to go through all of the trouble doing the maths, figuring out how much to add every time you test your pool then there’s actually an easier way to do it, and that’s by getting a salt water chlorinator like the Water TechniX Atomic Salt and Mineral Chlorinator! It’s as simple as it gets when it comes to pool chlorination! Simply plug it in, set your desired chlorine levels / power level and you’ll have your perfectly chlorinated pool day in and day out!

For more information on Pool Chlorine, we also have a chemical spotlight that you can check out here.

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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Written By

Timothy Te

Pool Guru at Mr Pool Man

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