Pool Chlorine Dose Calculator - How Much Should I Add To My Pool?

Need to add chlorine to your pool to lift the free chlorine level but not sure how much to add? Use this pool chlorine calculator to work out the right dose based on your pool and your chlorinating product!

It works with liquid chlorine, solid chlorine and granules.

Note: This pool is for routine chlorine addition. If you are planning on shocking your pool, use this chlorine shock calculator.

Why Chlorinate Your Pool?

Chlorine is one of the most important chemicals in your pool. That's because it kills bacteria, algae and other microorganisms in your pool that could make your very sick.

If you don't maintain an appropriate chlorine level in your pool, these microscopic organisms will grow rapidly and take over your pool, making it unsafe for swimming.

With that in mind, your next question is probably this: what chlorine concentration should I target?

What Is The Ideal Chlorine Concentration In A Swimming Pool?

Before we get ahead of ourselves and start talking about actual numbers, it's worth a quick recap on how chlorine works in swimming pools. There are 3 main forms:

• Free chlorine
• Combined chlorine
• Total chlorine

Free chlorine is the chlorine that is currently in the water and 'unreacted', that is, it's ready and available to kill bacteria or algae.

Combined chlorine is chlorine that has reacted with other compounds in the water like ammonium, to form chloramines. These chloramines are known as 'disinfection byproducts'.

Finally, there's total chlorine, which is simply the free chlorine plus the combined chlorine.

When we talk about ideal chlorine concentrations in swimming pools, we are most interested in the free chlorine concentration. Unfortunately, the combined chlorine is quite a weak disinfectant, so we can't rely on it to kill bacteria and algae for us.

Generally speaking, the ideal free chlorine concentration for a residential swimming pool is 2-4 ppm. Once your free chlorine starts dipping below 2 ppm (as measured by your test kit), you need to look at topping it back up.

This is backed by a variety of sources, including the SA government.

However, the ideal concentration is actually a little more complicated than this, and depends on your cyanuric acid (stabiliser) concentration too. New thinking suggests that for outdoor chlorinated pools, your free chlorine target should be 7.5% of your CYA concentration.

This is because higher CYA concentrations actually slow down how fast the free chlorine can attack and kill microorganisms. This is why it's not good to have too high a CYA, as it means your chlorine is less effective and you will require more.

The NSW guidelines are clear on this - public swimming pools with stabiliser must have higher free chlorine levels than those that don't use stabiliser.

How Much Chlorine To Add To Pool? (Liquid & Granular)

If you are wondering how much chlorine to add to your pool, the answer is: it depends. It depends on quite a few factors, including your pool's volume and current free chlorine concentration.

For example, if you have a 50,000 L pool with a current free chlorine concentration of 1 ppm that you want to lift to 3 ppm, you would need to dose 100 g of pure chlorine.

Most liquid chlorine is sodium hypochlorite, which has an available chlorine of 125 g/L, so you would need to dose 800 mL into your pool.

If you used solid chlorine granules in the form of calcium hypochlorite, with an available chlorine of 700 g/L, you would need to dose about 140 g into your pool.

If you used stabilised solid chlorine, such as trichloroisocyanuric acid, with an available chlorine of 900 g/L, you would need to add about 110 g into your pool.

As you can see, the amount of chlorine that you need to add per litre is quite variable. Use the calculator above to get a precise dose based on your pool conditions.

Consult this guide on liquid vs granular chlorine for help choosing the right type of chlorine for your pool.

How Do I Use This Pool Chlorine Calculator?

To use this chlorine calculator, simply enter the following information:

• Pool volume
• Current free chlorine level
• Target free chlorine level
• Chlorine type (solid or liquid)
• Available chlorine in product

Once you enter these values, the calculator will automatically calculate the required dose for you to properly chlorinate your pool and alleviate your low free chlorine problem.

Note that if your chlorine level is actually too high, you need to use a chemical known as a chlorine remover to lower it.