Is your pool pH too high but your total alkalinity just right? Not sure how to lower the pH without affecting your total alkalinity, or if it’s even possible?
This article will explain how to lower pH relative to total alkalinity in a pool, and how to prevent your pH from drifting upwards in the future.
The Challenge of Lowering pH Without Affecting Alkalinity
pH and alkalinity are very closely related, so reducing one will inevitably influence the other in the same direction.
As such, trying to lower pH without having any impact on total alkalinity just isn’t going to work in the long term. And the same applies in reverse; you simply can’t lower total alkalinity without also lowering pH.
So what’s the solution?
Fortunately, you do have more control when raising pH or total alkalinity, which means it’s technically possible to achieve this by lowering both and then raising total alkalinity.
How to Lower pH Without Lowering Alkalinity
Since lowering pH in your pool will always lower total alkalinity, you’ll have to take a two-pronged approach in order to achieve this.
Specifically, you will first need to use muriatic acid to lower both pH and alkalinity, then use baking soda to raise total alkalinity while minimally raising pH.
Here’s a step-by-step guide you can follow:
1. Test Your Water
You should always test your pool water before adding any chemicals, otherwise, you could end up overcorrecting.
In this case, since you’re going to be adding muriatic acid, you need to test your pH level and total alkalinity. The results of this test will help you figure out the correct amount of acid to add to your water.
Liquid test kits are more accurate than pool test strips, but either of these methods should give you a reasonably accurate reading.
2. Add Muriatic Acid to Lower Both
Once you know your pH and total alkalinity, you can accurately determine how much muriatic acid you need to add to bring it down.
To get an exact measurement, you have two options:
- Follow the usage instructions printed on your jug of muriatic acid.
- Use an online calculator (like this one), which will give you the dosage based on your pH and alkalinity inputs.
You can also add your acid in parts if you want a slower, more controlled approach, but this shouldn’t be necessary if your numbers are accurate.
When pouring muriatic acid into your pool water, apply it to the deep end of your pool, ideally directly in front of a return line while the pump is running. This will help circulate the acid into the water and prevent damage to surfaces.
3. Let the Acid Circulate for an Hour
Keep your pump running for up to an hour to help circulate the muriatic acid around the pool.
For safety reasons, it’s not recommended to swim during this time.
Once you’ve allowed enough time to pass, you’ll need to test your water again to make sure the pH has dropped to where you need it. If it hasn’t dropped low enough, add more muriatic acid and repeat this process until it has.
Note: Remember, your alkalinity will reduce alongside pH during this process. That’s expected, and we’re going to correct it in the next step.
4. Add Baking Soda to Raise Alkalinity
Now that your pH level is where you want it, the next step is raising the total alkalinity back to where it was.
In order to do that, you’re going to use regular baking soda (sodium bicarbonate) — and yes, this is the exact same stuff you find in pool store “alkalinity increasers”, just with fancy packaging.
Baking soda will have a significant and immediate effect on your total alkalinity while having a very small and delayed effect on your pH level.
To figure out how much to add, you can either add the baking soda in small increments or refer back to this calculator for an exact measurement.
As for adding it to your water, you can either add it directly in front of a return line or simply broadcast the powder across the surface of the pool.
5. Let the Baking Soda Circulate for an Hour
Once again, let the baking soda circulate for up to an hour.
It’s important to keep your pump on throughout this process to ensure maximum circulation.
As before, test your water again to make sure the total alkalinity has risen back to where it was prior. If it hasn’t increased enough, add more baking soda and repeat this process until it has.
Note: You may notice a small increase in pH after adding baking soda. This is nothing to worry about as long as you’re still within the ideal pH range (7.2 to 7.8).
How to Prevent Your Pool pH Rising
It’s normal for the pH level of your pool to slowly rise over time, especially if you have a saltwater pool.
Some common causes of high pH in pools include regular shocking, aeration from water features (or a saltwater generator), algae blooms, replastering of pool surfaces, or even just using high pH water to top off the pool.
The good news is, there are a few things you can do to prevent your pH from drifting upwards or at least slow it down.
Namely, these are:
- Lower your total alkalinity to reduce the acid-absorbing buffer it creates.
- Maintain proper sanitizer levels to kill algae (which feeds on carbon dioxide and ultimately increases the pH of your water).
- Limit the use of water features to slow your pH rising through excessive aeration.
- Use trichlor tablets (which are acidic) for your source of chlorine to help counter the natural rise in pH.
- Avoid using high pH household products like baking soda or borax to clean your pool.
- Test the pH level of your fill water before adding it to your pool (even if it’s just for occasional top-ups).
- If you want a more natural approach to lowering pH, consider injecting carbon dioxide (CO2) into your pool water.
Two Down, One Up.
It’s not possible to lower pH without lowering alkalinity, but with a bit of chemistry trickery, it’s possible to achieve the same end result.
All you need to do is lower both pH and alkalinity using a measured dose of muriatic acid, then follow it up with baking soda to increase total alkalinity back to where it was.
