How to Lower Alkalinity Without Lowering pH (In a Pool)



Is your total alkalinity too high but your pH is just right? Not sure how to lower alkalinity without affecting the pH, or if it’s actually possible?

This article will explain how to lower alkalinity relative to pH in a pool, whether or not it’s a good idea, and how to prevent your alkalinity from rising.

Do You Really Need to Lower Alkalinity?

Alkalinity (or total alkalinity) is a pH buffer with the sole purpose of absorbing changes in the water and stabilizing your pH level.

For most pools, the ideal range for total alkalinity is anywhere between 80 and 120 parts per million. This is the sweet spot for most pools where alkalinity keeps the pH level stable enough to keep everything in balance.

But the number itself isn’t important.

If your pH level is already ideal and doesn’t appear to be fluctuating very much, there’s no reason to adjust your total alkalinity because it’s already doing what it needs to do.

You’ll know if your total alkalinity is truly too high when your pH is no longer stable, and more specifically, starts to increase alongside it.

In short, if your alkalinity is high and your pH is constantly on the rise, that’s when (and only when) you should take action.

Why You Can’t Lower Alkalinity Without Affecting pH

If you need to lower your alkalinity, know it’s not going to be as straightforward as chucking in some “magical chemical”.

The problem with trying to adjust one of these values is that pH and alkalinity are very closely related. This is true to such an extent that lowering one will always eventually lower the other.

For that reason, attempting to lower alkalinity without having any effect on your pH level is just not realistic (the same way it’s not realistic to try and lower pH without lowering alkalinity).

Instead, the only way to truly achieve this is to lower both alkalinity and pH at once, then raise pH back up in isolation.

How to Lower Alkalinity Without Lowering pH

Remember, lowering alkalinity can only be done through lowering pH.

This process involves using muriatic acid to lower both pH and alkalinity, then using a process called “aeration” to raise pH back up in isolation.

Below is a step-by-step guide on how to do this:

1. Test Your Pool Water

Testing your water is always the first step when trying to correct your pool chemistry.

In particular, you need to know your water’s pH and total alkalinity readings in order to calculate exactly how much muriatic acid to add to your water.

It’s best to use a liquid drop testing kit for the most accurate readings, however, many pool owners manage to get by on the slightly less accurate (but more convenient) pool testing strips. Ultimately, either strips or drops will work.

2. Add Muriatic Acid to Lower pH and Alkalinity

With your pH and alkalinity readings in hand, you can start to figure out the dosage requirements for the muriatic acid.

Muriatic acid typically comes with instructions on how to measure it out, but some pool owners find it easier to use an online calculator for more precise measurement.

Either way, once you have the dosage down, pour the muriatic acid directly into your water. This should be at the deepest end of your pool, directly in front of a return line.

Your pool pump should also be left running to help circulate the acid and prevent it from concentrating in one area of your pool and potentially damaging your plaster or liner.

3. Allow Time for the Acid to Circulate

Wait about an hour for the muriatic acid to do its thing.

After that, go ahead and test your water again. You should see that your pH level is now very low (don’t panic, this is normal) and your alkalinity is about where it needs to be.

If your alkalinity is still too high, go ahead and add more acid until it falls in line with the recommended levels of 80ppm to 120ppm.

4. Aerate the Water to Raise the pH

Now, with your total alkalinity where you want it, you need to raise the pH back up to where it was prior to adding acid.

The only way to do this without also raising alkalinity is to use a process called “aeration” — which basically just means exposing more of your water to the surrounding air by forcefully disrupting the surface of the water.

Technical explanation: The more of your water’s surface area is exposed to air, the faster it outgasses carbon dioxide. Since carbon dioxide is acidic, reducing the amount of this substance in your water naturally leads to a rise in pH.

There are a number of ways to aerate pool water, such as:

  • Pointing your return jets upwards
  • Leaving water features running 
  • Running your saltwater generator (saltwater pools only)
  • Have people splash around in the pool

5. Allow Time for Aeration to Work

The time it takes for your pH to rise depends on which method you use, as some are more aggressive on your water than others.

For example, if you’re hosting a pool party with lots of splashing and pool games taking place, it may only take half a day to push the pH back up by the required amount.

Alternatively, if you’re just pointing your return jets upwards to create bubbles on the surface, you may need to leave them running for several days to have the same impact on pH.

How to Prevent Rising Alkalinity

It’s not uncommon to see your total alkalinity rise over time because pH naturally rises over time, and we know alkalinity always increases with pH.

In fact, the only way to prevent total alkalinity from rising in your pool is to prevent your pH level from rising.

Fortunately, the causes for rising pH are well established so it shouldn’t be difficult to maintain both your pH and alkalinity by taking some precautions.

In particular, you should:

  • Shock regularly to kill algae in your water, which consumes carbon dioxide and pushes up your pH level (similar to how aeration works).
  • Turn off your water features (waterfalls, spillovers, etc.) as often as possible to prevent unnecessary aeration.
  • Consider using low pH chlorine tablets to introduce a steady stream of acid into your water.
  • Avoid using high pH household products such as borax or baking soda to remedy your pool chemistry
  • Use lower pH fill water when filling or topping off your pool (always test first, whether you’re using city water or well water.)

Two Down, One Up.

While it may be impossible to lower alkalinity without lowering pH, it is possible to achieve the same outcome using a multi-step approach.

Simply lower both the pH level and total alkalinity using muriatic acid, then aerate the water by disrupting the surface for a prolonged period of time. It may even take several rounds, but it will get you there.

Categories: Pool Care, Pool Chemistry