Pool Alkalinity Calculator - How Much Chemical Should I Add To Adjust My Alkalinity?

Need to raise or lower your pool alkalinity but not sure how much chemical to add?

Use this calculator work out how much sodium bicarbonate (baking soda), sodium carbonate (soda ash), sodium bisulphate or hydrochloric acid is necessary to adjust your pool's alkalinity properly.

It can also calculate the final pH your pool will have after adding the chemicals.

Why Control Swimming Pool Alkalinity?

The total alkalinity of the water can have a variety of impacts on the health of your pool. However, it's primary purpose is to act as a buffer for the pH.

It prevents the pH from flying up and down in response to tiny changes in your pool water chemistry. With too little alkalinity, you would need to adjust your pool's pH constantly to keep it within the recommended range of 7.2 - 7.6.

With too much alkalinity, you would find that your pH is consistently high and difficult to shift back into the proper range.

So why all the fuss about maintaining a stable pH? An adequate pH is vitally important because it ensures that your chlorine is working properly (in unstabilised pools) and prevents corrosion of your pool surface and equipment.

It also ensures the safety of swimmers that use your pool, and prevents metal staining of your pool's surfaces.

What Is The Ideal Pool Alkalinity Concentration?

While the exact number for the ideal pool alkalinity concentration varies depending on who is doing the recommending, most agree that a range of 80 - 120 ppm is ideal.

Many government bodies actually recommend wider ranges than this. The NSW government recommends 80 - 200 ppm, while the SA government and NT government both recommend 60 - 200 ppm.

How Much Alkalinity Should I Add To My Pool?

The amount of alkalinity that you should add to your pool depends on your starting and final alkalinity concentrations, your pool volume, and the alkalinity chemical that you will be using.

Let's illustrate this with some examples.

Sodium Bicarbonate

If you have a 50,000 L pool with a starting alkalinity of 50 ppm that you want to increase to 80 ppm, you will need to add 2.5 kg of sodium bicarbonate (baking soda), assuming that you are adding pure baking soda.

If the pH started at 7.5, it will lift to 7.7 once the baking soda is added.

Use this baking soda calculator for more information.

Sodium Carbonate

If you have a 50,000 L pool with a starting alkalinity of 50 ppm that you want to increase to 80 ppm, you will need to add 1.6 kg of sodium carbonate (soda ash), assuming that you are adding pure soda ash.

If the pH started at 7.5, it will lift to 10 once the sodium carbonate is added.

As you can see, less sodium carbonate is required for the same increase in alkalinity, but it has a much greater impact on the pH.

Should I Adjust pH Or Alkalinity First?

It is much easier to adjust the alkalinity before adjusting the pH.

The relationship between the two is complex, but changing the alkalinity will have a big impact on pH, so it's best to adjust that first.

Once you've got the alkalinity just right, move onto adjusting the pH. Changing the pH is unlikely to have as much impact on the alkalinity, and it's the more important of the two to get right.

How Do I Use This Pool Alkalinity Calculator?

Here's what to do to calculate how much alkalinity to add to your swimming pool:

1. Enter your swimming pool volume. If unknown, click the checkbox for help calculating it.
2. Enter your current pH.
3. Enter your current and desired total alkalinity concentrations (in ppm or mg/L).
4. Select the product you will be using to raise or lower the alkalinity. If raising, you can choose from sodium bicarbonate or sodium carbonate. If lowering, you can choose from sodium bisulphate or hydrochloric acid.
5. Enter the concentration of your selected product.

Once you've done this, the calculator will work out exactly how much product you need to add to adjust your pool alkalinity to your desired level.

It will also tell you the final pH that your pool will end up with.