How Much Hydrochloric Acid To Add To Pool - Calculator

Need to drop the pH in your swimming pool but not sure how much hydrochloric acid to dose? Use this hydrochloric acid calculator to work out how much acid you need to add to your pool!

Warning: The interaction between acid, alkalinity and pH is notoriously complicated, and depends on the other chemicals already in your pool, as well as the water temperature. Consider the numbers below a rough estimate only.

Only dose half of the amount the calculator recommends into your pool, then allow 2-3 hours of mixing (with pump on) before retesting pH/alkalinity and re-dosing.

Never dose more than 500 mL of hydrochloric acid into the pool at once.

Why Use Hydrochloric Acid In Your Pool?

The primary use of hydrochloric acid (aka muriatic acid) in swimming pools is to lower alkalinity and pH. High alkalinity in your pool can be a problem for a variety of reasons, as can high pH (it can render your unstabilised chlorine ineffective, for one).

Hydrochloric acid is a strong acid that releases H⁺ ions into your pool water, which react with the alkalinity to neutralise it and simultaneously lower the pH.

Here are the main benefits of using HCl in your pool:

• Inexpensive
• Easy to obtain
• Very effective at lowering pH and alkalinity

However, it doesn't come without its drawbacks:

• Dangerous to humans when not diluted - wear gloves and goggles when handling!
• Can easily overdose and lower your pH too much
• Can damage pool surface if not mixed into the water properly

How Much Hydrochloric Acid Should I Add To My Pool?

The right amount of hydrochloric acid for your pool is highly dependent on your volume, total alkalinty and pH. There's no one-size-fits-all recommendation here - that's why I've made this calculator!

Here's an example. Say you have a 50,000 L pool with a pH of 8 and a total alkalinty of 120 ppm.

To reduce your pH to 7.4, you would need to add about 700 mL of 30% hydrochloric acid. This would have the additional effect of lowering your alkalinty to 112 ppm.

Another example: Take a 30,000 L pool with a pH of 8.3 and a total alkalinity of 150 ppm.

To reduce the pH to 7.4, you would need to add about 800 mL of 30% hydrochloric acid. This would lower the alkalinity to 135 ppm.

Note that this calculator does not consider the pH impact of CO₂ off-gassing over time. Even though after adding the acid your pH will initially be 7.4, the CO₂ in the water will off-gas over time, which will result in your pH slowly rising again.

It won't rise back to where it started, but it will lift a little.

How Do I Use This Hydrochloric Acid Pool Calculator?

For this calculator to accurately calculate your hydrochloric acid dose, you will need to enter the following:

• Pool volume (in L)
• Current pH
• Current alkalinity (in ppm or mg/L)
• Desired alkalinity (in ppm or mg/L)
• Hydrochloric acid concentration (in %)

Once you have entered these, the calculator will be able to accurately determine how much hydrochloric acid is necessary to reach your target alkalinity. It will also let you know the impact that this will have on pH.

How Do I Add Hydrochloric Acid To My Pool?

Here's what you'll need to safely add hydrochloric acid to your pool:

• Safety goggles
• Safety gloves
• Hydrochloric acid
• Measuring cup
• Bucket (at least 10L volume)

Once you've gathered these items, here's the steps to take to add the acid to your pool:

1. Take a measurement of your pool's pH and alkalinity using a test kit or some test strips.
2. Use the calculator above to work out the right dose for your pool.
3. Head out to the pool. Make sure there aren't any children or pets at the pool with you. Close the pool gates.
4. Put on your safety goggles and gloves.
5. Fill the bucket up halfway with water from your pool.
6. Pour out the dose of hydrochloric acid you calculated earlier into the measuring cup. If the calculated dose exceeds 500 mL, only pour 500 mL into the measuring cup. You can add the rest later. Be aware that the fumes from the hydrochloric acid can be dangerous and shouldn't be inhaled. Make sure you are in a well ventilated area.
7. Pour the acid from the measuring cup into the bucket of pool water carefully, making sure that none of it splashes out onto you or the pool surface.
8. Without stirring the bucket contents, slowly pour it into the pool while walking around the perimeter.
9. Leave the filter and pump running for a few hours, then re-test the water for pH and alkalinity. If necessary, repeat these steps with additional doses until you achieve your desired pH.

Still have questions? Have feedback on the calculator? Get in touch with me over at the contact page!