pool-chlorine

Pool Chlorine: Everything You Need To Know [Buyers Guide]

So, you want to learn about chlorine?

Great, you’re in the right place. 

Nipping down to the shop to stock up on your pool chlorine supply can quickly turn into a lengthy expedition once you hit the aisles: there are just so many options.

Is it really all that important, anyway?

Well, yes. Chlorine is an important part of keeping your pool clean, your equipment working and your swimmers safe. 

In this guide to pool chlorine, we’ll cover:

  • What pool chlorine does and how it works
  • How to test for pool chlorine correctly
  • Types of chlorine for pools
  • Get in touch for help

Let’s dive in.

What Does Pool Chlorine Do?

Pool chlorine helps prevent your pool from getting dirty, protecting your swimmers and your equipment. 

As soon as chlorine is added to your pool, hypochlorous acid kicks into gear. 

Breaking down into hypochlorite, this compound oxidises organic microorganisms like algae spores, bacteria, and viruses, stopping them from growing and taking over. 

It’s easy for these microorganisms to reach your pool from the wind, flora and fauna around it, contaminated rainwater, and swimmers.

So it’s important to stop them in their tracks as quickly as possible.

Maximise the impact of your chlorine

Pool chlorine works best in conjunction with two other products:

  1. Stabiliser – to prevent the chlorine from evaporating, and,
  2. Shock – to manage the chloramines that result from chlorine doing it’s job. 

Here’s how they work.

stabiliser-chlorine-shock

Chlorine evaporates very quickly in direct sunlight, but this reaction is slowed down with the stabiliser. The addition of a stabiliser gives the chlorine a chance to work. 

After chlorine successfully destroys a microorganism, it sometimes turns into a chloramine.

Chloramines (combined chlorine) will not sanitise your pool, they have a strong smell, and can irritate the eyes and skin of your swimmers.

So you’ve got to get rid of them by breaking them down with a high concentration of chlorine, such as a shock treatment.

Fortunately, you may not need to buy three different products. Some are available which combine the chemicals for maximum impact. 

There are a few things you’ll need to do first.

Does Your Pool Need Chlorine? Test It First

Always make sure your pool actually needs a chlorine top-up by reading the chlorine level using a test kit.

The objective of testing is to determine free and total chlorine levels.

Free chlorine is chlorine that can still sanitise. 

Total chlorine is a combination of free chlorine and combined chlorine (chloramines, the stuff you don’t want anymore).

You can determine whether there are chloramines in your pool when the total chlorine reading is higher than the free chlorine reading. 

In this case, you’ll need to shock your pool.

You can add additional chlorine to your pool if the free chlorine reading is below 1ppm or if you want to slightly increase free chlorine up to 3ppm.

Here are some guidelines about chlorine ppm levels.

  • Too low: 0ppm – 0.5ppm. It’s time to add chlorine and you could increase your regular dose.
  • Ideal: 1ppm. No action required, maintain your current dose.
  • Fine: 1.5 – 3ppm. No action required, but you may want to slightly decrease your dose.
  • Too high: above 3ppm. Avoid swimming and test again until your free chlorine has decreased. 

To add the right amount of chlorine to reach the desired level, you’ll need to calculate how many litres of water (volume) your pool holds using a volume calculator.

Then, read the chlorine manufacturer guidelines for correct chlorine measurements.

Preparing Your Pool

Once you know your pool’s levels, you’ll need to balance the other chemicals as below:

    • Pool pH: 7.2 – 7.8
    • Total alkalinity: 80ppm – 120ppm
    • Calcium hardness: 150ppm – 250ppm

Pool pH and chlorine levels are intertwined. 

Chlorine effectiveness decreases in water with a pH higher than 7.8 and increases with a pH closer to 7.2.

So don’t let all of your hard work go down the drain: pay attention to what you’re adding and when.

Last of all, sanitise your pool with chlorine while the sun is down, as UV rays can destroy chlorine before it even enters your pool.

Choosing Which Type Of Chlorine To Use

Pool chlorine comes in many different forms: liquids, granules, and tablets, to name a few.

Here, we’ll break down what they are and why you might choose them.

Liquid pool chlorine

Sodium hypochlorite is the active ingredient in liquid pool chlorine. It has a high pH of around 13 and a low chlorine concentration of 12%.

Sodium hypochlorite is the active chlorine ingredient in household bleach, just at half the concentration of liquid pool chlorine. 

Liquid pool chlorine is generally used in commercial pools. It requires storage in specialised tanks in a well-ventilated area and is dispensed via an automated liquid chlorine dispenser.

Therefore, you’ll rarely come across liquid chlorine that is ready for use in residential pools.

But when you do, it’s typically the cheapest option.

After extraction from its special storage, liquid chlorine is also easy to use as it doesn’t need to be mixed or diluted – just measured and poured directly into your pool.

How to add liquid chlorine to your pool
  1. Switch on: Make sure your filtration system is running.
  2. Cover up: Put on a pair of gloves, some old clothes and goggles.
  3. Prepare: Get a measuring jug and your liquid pool chlorine ready.
  4. Measure: Carefully measure the correct dosage of liquid chlorine.
  5. Pour: Tip the liquid chlorine directly into the deep end of your pool.

NB: Never pour liquid pool chlorine straight into the skimmer, or anywhere else for that matter, except for the deep end of your pool.

Pool chlorine granules

Pool chlorine granules can be purchased containing either dichlor (sodium dichloroisocyanurate) or cal hypo (calcium hypochlorite) as the active ingredient.

Dichlor granular pool chlorine has a low pH of around 6.5 and a medium chlorine concentration of 50%.

It’s easy to use, dissolves rapidly, and also comes stabilised, meaning that the chlorine will evaporate a lot slower.

Cal hypo granular pool chlorine has a high pH of around 12 and a high chlorine concentration of 65%.

Cal hypo is a great way to safeguard pool equipment from corrosion caused by calcium deficiency. It’s the more cost-effective sanitiser, but as it’s unstabilised, you’ll need to be more cautious.

Pool chlorine granule products

All granular pool chlorine needs to be measured and mixed in a bucket of water before adding it into your pool to ensure proper chlorine distribution.

How to add chlorine granules to your pool
  1. Switch on: Make sure your filtration system is running.
  2. Cover up: Put on a pair of gloves and goggles.
  3. Prepare: Get a large bucket of water and your granular pool chlorine ready.
  4. Measure: Carefully measure the correct dosage of granular chlorine into the water.
  5. Mix: Dissolve the granules by mixing with a long stick.
  6. Pour: Carefully tip the chlorine around the deep end of your pool.

Tips when using granules:

  • Make sure you’re not using pool chlorine granules on a windy day and follow safety instructions carefully.
  • Never pour the water containing dissolved chlorine granules straight into the skimmer, only into the deep end of the pool.

Pool chlorine tablets

Trichlor (trichloroisocyanuric acid) is the active ingredient in pool chlorine tablets. It has a low pH of around 2.9 and a high chlorine concentration of up to 90%.

Trichlor is chlorine as a solid and comes in the form of one or three-inch discs or sticks.

Pool chlorine tablet products

Floating tablet dispensers are placed directly into your pool. You’ll need to keep a watchful eye on them to ensure they don’t get stuck.

If you’re looking for something that requires a little less maintenance, consider investing in an inline chlorinator. It automatically dispenses fully dissolved chlorine into your pool.

How to add pool chlorine tablets to your pool
  1. Switch off: Make sure your filtration system isn’t running.
  2. Cover up: Put on a pair of gloves and goggles.
  3. Prepare: Get your tablets ready.
  4. Open: Carefully open the chlorinator ensuring you don’t inhale any fumes.
  5. Measure: Put the pool tablets into the chlorinator or dispenser. 
  6. Close: Secure your chlorinator or dispenser. 
  7. Switch on: Turn your filtration system back on.

NB: Pool chlorine tablets usually take around seven days to fully dissolve.

Make sure that you never overfill an inline chlorinator with too many chlorine tablets.

Salt chlorinator

A salt chlorinator uses salt and electrolysis to create sodium hypochlorite.

It’s basically a liquid pool chlorine generator.

But unlike sodium hypochlorite in the form of liquid pool chlorine, salt stores well and doesn’t lose efficacy.

When comparing a salt chlorinator versus pool chlorine, it essentially comes down to whether you would like automatic or manual chlorine sanitation.

Of course, the initial purchase of a salt chlorinator can be costly.

However, you’ll spend less time manually sanitising and shocking your pool.

A salt chlorinator will produce chlorine, and the high chlorine concentration inside it will remove many of the chloramines.

You can even upgrade a chlorinator to automatically test pool pH, control water temperatures, and remotely control other pool equipment.

Salt chlorinator products

If you’d like to learn more, check out our comprehensive guide on salt chlorinators.

Still Unsure About Chlorine? Not For Long

You and chlorine will one day be on the same side: allies working together to protect your pool and keep swimmers out of harm’s way.

But on some days, it can feel as though chlorine just isn’t on your side.

So, if you need some help to master chlorine usage, don’t hesitate to contact us for guidance or get in touch with your local pool store.

About the author

Adrian Hill

Adrian Hill

Hey! I'm Adrian, founder and pool expert here at Dolphin Pacific. I love spending time with family, fishing, and have been known to brew my own beer.

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