How to Lower pH In a Pool (Follow These 6 Easy Steps)



Is the pH in your pool too high?

Are you looking for the easiest and most efficient ways to reduce your pH level without upsetting the rest of your pool chemistry?

We’re going to walk you through using various chemicals to lower your pH level, the pros and cons of each, and how to prevent or slow down your pool’s pH from continuously rising.

When is pH too High?

pH measures the acidity of your pool’s water.

This is a scale of 1 to 14, with 1 being highly acidic, and 14 being highly basic. Right in the middle is neutral, at a pH of 7.

Pool water is best kept at a pH level of 7.2 to 7.8, or slightly basic.

When your water becomes too basic, however, it leads to cloudier water, weakened sanitizer, scaling of pool surfaces, and just general discomfort on your skin and eyes.

In short, if the pH level in your pool exceeds 7.8, you should take action in reducing the pH in order to prevent complications with your water.

What Chemical is Best for Lowering pH?

If you want to lower the pH in your pool, you need to use a low pH chemical, otherwise known as an acid.

The acids most commonly used in pools are:

For most pools, the best acid to use is muriatic acid.

Both dry acid and sulfuric acid add sulfates to your water, which, at high levels, can lead to a number of issues.

While not as problematic for vinyl pools, sulfates can damage concrete or plaster pool surfaces, be corrosive to metal pool parts and fixtures, and even degrade your saltwater generator if you have a salt pool.

Muriatic acid doesn’t contain sulfates or any other additives, making it the cleanest and most efficient acid for the job.

Note: Cyanuric acid is also often used in pools to stabilize the chlorine. While it does lower pH, it should never be used primarily for that purpose because too much cyanuric acid will reduce the sanitizing power of chlorine.

How to Lower pH in Your Pool (6 Steps)

This section will take you through a step-by-step process for lowering the pH in your pool without upsetting your pool chemistry.

Here’s what you’ll need:

  • A pool testing strip or liquid test kit
  • A jug of muriatic acid (or dry acid)
  • Safety gear (gloves and goggles)
  • A standard tape measure
  • A calculator (or your phone)
  • A box of baking soda (maybe)
  • A dash of patience

1. Test Your Water

Whether you’re lowering or raising your pH level, you must always test your water prior to making any changes.

This will tell you exactly how far off you are from the ideal pool pH level, which is anywhere between 7.2 and 7.8, and ultimately how much acid you need to add to get back down into that range.

You will also need to know your current total alkalinity, as this will play a part in calculating the correct dose of acid (we’ll cover that soon enough).

A test strip will be accurate enough to get your readings, but a liquid test kit will give you the most precise results if you have one handy.

2. Calculate Your Pool Volume

We just need one more number before you start measuring out the acid dosage, and that’s your pool volume.

If you already know how much water your pool holds (in gallons), you can skip this step, otherwise, you’ll need to whip out your tape measure and calculator.

For rectangular or square pools:

  1. Measure the length, width, and average depth of your pool (in feet)
  2. Multiply the length by the width, then multiply by the depth
  3. Take the number you end up with and multiply that by 7.5

For round pools:

  1. Measure the diameter of your pool (in feet)
  2. Multiply the diameter by itself (diameter x diameter)
  3. Take the number you end up with and multiply that by 5.9

Note: You can also use a pool volume calculator to do the sums for you, but you’ll still need to input your pool measurements.

3. Measure Out Your Acid

At this stage, you should have your current pH level and total alkalinity readings, as well as your pool volume in gallons.

Now, plug those numbers into this pool chemistry calculator. This will calculate the exact acid dosage to add to your water in order to lower your pH by just the right amount.

To use the calculator:

  1. Enter your pool size (at the top)
  2. Enter your current pH level in the pH section
  3. Set your target pH level to a value between 7.2 and 7.8
  4. Enter your current total alkalinity in the TA section
  5. Set your target alkalinity to a value between 80 and 120ppm
  6. Note the acid dosage instructions (we recommend muriatic acid)

To give you an idea of how much acid you might need, below are the average pH adjustments per 10,000 gallons:

  • 10 oz of 15% strength muriatic acid will lower pH by 0.1
  • 5 oz of 31% strength muriatic acid will lower pH by 0.1
  • 7 oz of dry acid will lower pH by 0.1

Important: Using any acid in your water will also lower total alkalinity, this is unavoidable. If your alkalinity falls too much during this process, don’t panic; we will correct the alkalinity in the last step.

4. Add the Acid to Your Water

With your dosage nailed down, it’s time to add it to your water.

Depending on how confident you are with your numbers, you may want to be conservative and use 75% of the dosage first. You can always add the rest if needed.

If you’re using muriatic acid, simply measure the liquid and pour it directly into the deepest area of your pool near an active return jet. Some pool owners prefer to dilute muriatic acid beforehand, but that really isn’t necessary.

If you’re using dry acid, however, dissolving the granules in a bucket before adding it to the water is recommended. Once dissolved, pour it into the deepest end of your pool near an active return jet.

Important: Regardless of which acid you’re using, be sure to use protective equipment such as gloves and goggles before handling.

5. Retest Your Water (After 15 Mins)

Acid works very quickly in pool water so you won’t have to wait long for the changes to take effect.

Assuming you keep your pool pump running to allow proper circulation (highly recommended), you can safely test the water after around 15 minutes.

Once again, you can use either a test strip or liquid drop kit, though the liquid kits are considered to be more accurate. Regardless, it’s a good idea to stick with the same kit used in step 1.

You should see a much lower pH and total alkalinity reading compared to your first result, hopefully in the ideal range for both:

  • pH level between 7.2 and 7.8
  • Total alkalinity between 80 and 120ppm

If you need to add more acid, go ahead and do that now.

For now, just give priority to getting your pH level in range as we can easily bring your alkalinity back up if necessary. Don’t proceed until your pH level is where it needs to be.

Pro tip: If you accidentally lowered your pH by too much, use a small amount of soda ash (washing soda) to bring it up again. If you want to raise pH without raising alkalinity, you’ll need to aerate your water instead.

6. Add Baking Soda (If Necessary)

Since acid lowers both pH and alkalinity, it’s possible your total alkalinity is now below the recommended minimum of 80ppm.

If that’s the case, there’s an easy fix.

Baking soda (sodium bicarbonate) raises total alkalinity while having almost no impact on pH, so it’s perfect for situations where you need to raise alkalinity in isolation…. like this one.

You can refer back to this chemistry calculator to figure out how much baking soda to add, but as a general guide:

  • 5 oz of baking soda will raise total alkalinity by 2ppm
  • 14 oz of baking soda will raise total alkalinity by 5ppm
  • 27 oz of baking soda will raise total alkalinity by 10ppm

Note: Baking soda will increase pH by a very, very small amount. Too small to make any noticeable difference in this case.

Why High pH is Bad News

Knowing how important pH is to your pool chemistry, it’s unsurprising what happens when it comes out of balance.

These are the side effects of pool water that’s too basic (high pH):

  • It weakens your sanitizer. Chlorine sanitizing power is strongest at lower pH levels, so as your pH rises, your water becomes less protected against contaminants like algae.
  • It scales your surfaces. High pH causes the calcium in your water to fall out of solution, which leads to staining on surfaces known as calcium scale. This effect is worsened if you have high calcium levels.
  • It makes your water cloudy. As pH rises and calcium falls out of solution, it floats around in your pool water causing it to appear murky or cloudy, especially with higher calcium hardness.
  • It’s harsh on skin and eyes. Very high pH water can begin to irritate your skin and eyes, though, oftentimes, the real culprit is a build-up of used chlorine in the water (called chloramines).
  • It makes pH harder to adjust. High pH causes high alkalinity (they’re closely related), and since alkalinity is a pH buffer, this ultimately makes it harder to adjust your pH level.

Note: The severity of these side effects depends largely on the LSI of your water; a measurement that extends beyond just pH.

Why Your pH is High (And How to Prevent It)

If you’ve tested your water and the results show a high pH level, it was probably caused by one or more of the following:

  • You shocked your pool. The most common type of pool shock, calcium hypochlorite, is very high in pH. It’s normal to see a spike in your pH level as well as your calcium hardness level.
  • You have algae. Algae gobble up carbon dioxide in the water, which, similar to water aeration, slowly causes your pH level to rise because carbon dioxide is an acidic compound.
  • You accidentally used a pH increaser. Chemicals like soda ash and borax are high in pH, and are sometimes used in pools for other purposes. Borax, for example, can be be used to clean pool stains.
  • You used high pH water. Whether you’re filling or topping off your pool, always test the source water for pH before assuming anything. Well water may also be highly saturated.
  • You have water features. Water features create a lot of movement and splashing in your pool, this speeds up aeration (the outgassing of carbon dioxide), which ultimately raises pH.
  • You have a salt pool. Similar to how water features raise the pH level, saltwater generators create lots of bubbles during the conversion of salt to chlorine, which acts as another form of aeration.
  • You replastered your pool. New plaster releases calcium hydroxide for up to a month. This substance has a pH level of 12, naturally pushing your pH up when absorbed by the water.
  • Your alkalinity is high. Total alkalinity is a measure of all dissolved alkaline substances in the water, so the more you have, the more basic your water will eventually become.

What Goes Up, Must Come Down.

A high pH level isn’t good for your pool, so taking steps to recognize and deal with a rising pH should always be top of mind.

The good news? As long as you have a test kit handy and a calculator to boot, you can easily lower the pH level in your pool using a measured dose of muriatic, dry, or sulfuric acid.

Categories: Pool Care, Pool Chemistry