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How to Lower Alkalinity in Pool Without Affecting pH

So perhaps you’ve been looking to lower the alkalinity of your pool, but realize that lowering the usually causes the pH to drop too. In this article, I’ll be showing you the best chemicals and methods to get your alkalinity and pH to where it needs to be.

It’s not possible to lower the alkalinity without also affecting or lowering the pH. Instead, the best thing you can do is to lower both the pH and alkalinity using muriatic acid or sodium bisulfate, then aerate the water or add soda ash to increase the pH back up.

Before we get into the methodology of reducing alkalinity and pH and then raising the pH back up, let’s first take a look at why we should do this in the first place, as it’s equally important for you to understand the dangers of high alkalinity.

Lower Alkalinity in Pool Without Affecting pH

Causes of High Alkalinity in Pools

Several factors, such as the use of hydroxides and fill water, can contribute to high alkalinity. Here’s a list of some of the most common culprits behind high alkalinity levels:

  • Using of baking soda makes large pH increases
  • You’re filling your pool with high alkalinity fill water
  • You’ve recently plastered your pool
  • The water’s pH is too high
  • Other factors can be found here

Why High Alkalinity in Pools is Bad News

Because alkalinity is heavily associated with pH, when you have higher than normal alkalinity levels, that can result in a wide array of problems stemming from both the alkalinity and the pH. As such, you should be aware of them since they can indicate an issue with your water chemistry.

Here’re some of the most common issues to be aware of:

  • It can reduce your chlorine’s effectiveness
  • It can cause physical irritations such as red and irritated eyes, dry skin, and itchy scalp
  • A reduction in chlorine effectiveness can result in cloudy water, algae buildup, and calcium buildup
  • Filters can become more vulnerable to wear and tear
  • Scale buildup can occur

Can You Lower Pool Alkalinity without Lowering pH?

Simply put, it’s impossible to simultaneously lower pool total alkalinity and leaves pH the same since lowering one will always eventually lower the other.

There is a relationship between alkalinity and pH that can’t be altered. They usually always follow each other.

Related Reading: How to Lower Alkalinity | Pool Alkalinity High

Why Does pH Go Down with Alkalinity?

Let’s look at this in further detail.

Alkalinity essentially buffers the pH and tries to prevent it from lowering. It gives the water the ability to neutralize acids (buffering). Alkalinity is made up of carbonates, bicarbonates, and other substances.

So to lower the pH we must reduce the alkalinity.  This is why pH goes down when lowering alkalinity.

In pools and hot tubs (spas), sodium bisulfate or muriatic acid are generally used to decrease alkalinity, which then reduces pH. These are both acids.

By adding acid, it converts the bicarbonates, which make up part of the alkalinity, into carbonic acid (H2CO3 aka dissolved CO2). It’s this change that will lower the pH.

The higher the total alkalinity, the more acid is needed to reduce the pH.

Related Reading: What is Total Alkalinity in Pools | pH vs Alkalinity

What if Pool Alkalinity is High but pH is Not?

So what do you do then? Now you know it’s not possible to lower alkalinity without lowering pH.  How do you get both the alkalinity and pH to the correct levels then?

There’s a simple solution. It’s possible to raise pH by itself while keeping alkalinity the same.

Therefore, the trick is to lower both first before raising the pH back up to normal levels.

Here’s what to do if alkalinity is high but not pH:

Step 1: Lower alkalinity using sodium bisulfate or muriatic acid. This will usually result in the pH being a little low.

Step 2: To increase the pH but not the alkalinity, aerate the water or use a little soda ash.

We’ll go into more details below…

Related Reading: How to Raise Pool pH Without Raising Alkalinity (TA)

Ways to Reduce Alkalinity in a Pool

First, let’s go over the steps of reducing alkalinity using muriatic acid. You can also use sodium bisulfate, but we’ll cover that later.

Naturally, the pH will go down along with the alkalinity, but let’s not worry about that just yet. We’ll go over how to raise the pH back up later on.

Materials Needed to Lower Alkalinity

Here’s a list of the things you’ll be needing to lower the alkalinity:

Taylor Technologies Pool / Spa Test Kit K-2006
  • Tests total alkalinity, free/combined chlorine, cyanuric acid, calcium hardness & pH
  • Extremely accurate (better than test strips)
  • For pools & spas
We're industry experts and only recommend products we would use ourselves. If you click this link, we may earn a commision at no additional cost to you.

Steps to Lower Alkalinity

Here are the steps to lowering the alkalinity in your pool using muriatic acid, like this one:

Muriatic Replacement Acid
  • Same powerful cleaning properties as muriatic acid, but with added benefits
  • Reduces the risk of corrosive damage to surfaces
  • Effective alternative to traditional muriatic acid
  1. Test the pool water then turn off the pool pump and wait for the water to settle
  2. Calculate the amount of muriatic acid necessary to add to the water (generally, it takes 25.6 ounces of full-strength muriatic acid to reduce the alkalinity of a 10,000-gallon pool by 10 ppm).
  3. Pour the muriatic acid into the deepest part of your pool and let it remain there for an hour.
  4. Turn on your pool pump and let it run for 5 hours
  5. Test your pool water alkalinity and then pH level

Related Reading: Using Sodium Bisulfate to Lower pH & Alkalinity in Pool

Other Products to Try

Besides muriatic acid, another option you can consider using to lower the alkalinity level is sodium bisulfate. It is sometimes referred to as acid salt or dry acid and may be sold as pH down, pH reducer, pH minus, or pH decreaser.

Sodium bisulfate is sometimes considered a better alternative than muriatic acid because, unlike muriatic acid, it’s much safer for both yourself and the pool. 

Unlike muriatic acid, which is usually found in a liquid form and thus is susceptible to splashing, sodium bisulfate comes in a granular form, thus making it less prone to splash or spill.

While it is indeed safer and more user-friendly than muriatic acid, sodium bisulfate does come at a cost, literally. It is much more expensive to buy. In addition to its cost, sodium bisulfate is also not as reactive as muriatic acid, thus it takes longer to do the same job.

However, if safety is of concern to you and you don’t mind the extra waiting and potential extra doses, then sodium bisulfate should be something for you to consider.

How to Raise the pH Back Up Once You’ve Lowered the Alkalinity

Now that your alkalinity is down to normal levels, you may now find your pH is too low. So it’s time to raise the pH back up to normal using either aeration or soda ash. Here’s how they work.

Increasing pH via Aeration

Aeration is when you expose more of the water to the surrounding air by disrupting the water surface. This causes the water to outgas carbon dioxide, which is acidic, thus reducing the acidity and causing a rise in pH.

Here are some ways of aerating your pool water:

  • Pointing your return jets upwards
  • Leaving any water features running (waterfalls etc.)
  • Rain – but unless you’re God…
  • If you have a salt pool, running the saltwater generator
  • Splash around in the water
  • Using an air compressor in an aeration nozzle
Swimming pool with return jets bubbling and aerating the water.
Using the return jets will raise pool pH by aeration.

The amount of time it takes to aerate the water depends on your method. For example, you may increase your pH from 7.0 to 7.2 overnight when leaving the return jets on.

The more disruptive it is, the quicker it’ll aerate the water and the pH will drop.

Increasing pH via Soda Ash

Sodium carbonate, or soda ash, is a well-known way to increase pH while slightly raising alkalinity. It’s a better alternative to baking soda, which primarily raises alkalinity, however, it’s still going to slightly raise it due to sodium carbonate being a component of total alkalinity.

Duda Energy Sodium Carbonate
  • May be used for water softening
  • Oil absorbent
  • Adjusts pH level

Though easier and less time-consuming than aeration, soda ash is not as widely used since, at the end of the day, it’s still going to raise the alkalinity slightly.

Of course, because you only want to lower your alkalinity once the pH has also risen if the pH has decreased back down to its normal range along with the alkalinity, there’s no reason for you to aerate your pool or use soda ash.

Related Reading: Soda Ash or Baking Soda for Pool | Which is Better?

Tips to Prevent High Alkalinity

The only real way to prevent alkalinity from rising in your pool is to prevent pH from rising. There are several ways you can go about doing this:

  • Regularly shock your water to kill algae. Algae consume carbon dioxide and cause pH levels to rise.
  • Turn off water features whenever possible to prevent unnecessary aeration.
  • Use low pH chlorine tablets.
  • Don’t use high pH household products like borax or baking soda
  • Use lower pH water when filling up your pool

Final Thoughts

Though it’s not possible to lower alkalinity while keeping your pH unaffected, rest assured that there are several ways to raise pH once the alkalinity is back to normal. And be even more restful knowing that once you’ve adjusted your alkalinity and pH, there are many proven ways to prevent you from having to adjust them again.

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