Using Muriatic Acid In Your Pool: How to Lower Alkalinity, pH, and More Questions Answered

Written by Michael Dean
February 7, 2024

muriatic acid next to a swimming pool

Muriatic acid is a common chemical used in swimming pools to lower alkalinity and pH levels in your pool water. You may have seen it in your local hardware store because you can use it for a variety of other projects around the house too. However, when it comes to your pool, this acid can not only lower alkalinity and pH levels but can also clean your filter and help remove stains from your pool surfaces. I’ll cover all of this and more in the guide below. Let’s get started!

Main Takeaways

  • Muriatic acid is a handy chemical that can lower your total alkalinity and pH, clean filters, and remove concrete pool surface stains.
  • Always protect yourself and wear proper PPE gear when handling muriatic acid.
  • Muriatic acid will lower both alkalinity and pH, but they may decrease at different rates.

What is Muriatic Acid?

Acid refers to anything with a pH of 7 or less. Muriatic acid is a form of hydrochloric acid that is more diluted, with a pH of 1-2. Acids are found in citric fruits, vinegar, soft drinks, and even vitamins (many acids are also handy natural pool cleaners).

Pool owners use muriatic acid to clean the surfaces and maintain the proper pH levels in swimming pools.

What Does Muriatic Acid Do For a Pool?

To address an alkalinity imbalance, you will need to use muriatic acid. Muriatic acid is a milder acid, making it perfect for treating swimming pool water as it will help lower the total alkalinity and even the water’s pH level if it gets too high. Be sure to buy chemicals specifically for treating swimming pools to have the optimal concentration of muriatic acid.

Muriatic acid is also a great cleaning agent for pool surfaces (like tiles) and filters. It can clean cartridge filters and DE grids, as well as remove concrete pool surface stains and break down stubborn algae.

How Can Muriatic Acid Help Lower Alkalinity and pH Levels?

Alkalinity levels decrease over time, and when you adjust the alkalinity, you also lower the pH level. Keep it between 7.4 and 7.6 to maintain a balance. And by using our pool alkalinity calculator to assist you, aim to bring the alkalinity level as close as possible to 125 ppm.

Changing your alkaline levels is not as easy as expected. Sometimes, you will create a pool of water that has low pH and high alkaline. This situation frequently happens if you use a chlorine stabilizer, which contains cyanuric acid.

For the best results, it’s best to adjust pH and alkaline levels in stages. Consider adding chemicals slowly, according to a paper on chemical adjustment.

Step-by-Step: How to Add Muriatic Acid to Your Pool to Lower Pool Alkalinity and pH

Here is the step-by-step approach if you want to lower your alkalinity and pH levels by yourself.

Step 1: Test Your Total Alkalinity and pH Levels

Record the results using a pool water testing kit. Write down the target alkalinity. Your target level for alkalinity is 120 ppm. However, if you’ve noticed a recurring problem with high alkaline, go for a slightly lower target of 100 ppm instead. Your target level for pH is between 7.2 and 7.6.

pH scale

Step 2: Protect Yourself When Handling Acid

Undiluted muriatic acid is hazardous. Always wear proper protective gear (gloves, eyewear, and full-coverage clothing) when handling the substance.

Step 3: Calculate How Much Muriatic Acid To Add

Use my pH calculator to determine how much muriatic acid to add, according to your current pH level.

If you don’t already have some muriatic acid, I recommend picking it up at your local pool supply store. Hardware stores may have it, but it might not be pool-grade. Muriatic acid can be difficult to order online since it’s a hazardous material, but the brand I listed below is a decent option.

Acid Blue Muriatic Acid

You can use this pool-grade muriatic acid to lower alkalinity and pH in your swimming pool.

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I may earn a commission if you make a purchase, at zero additional cost to you. This in no way impacts my research process or opinions.

Step 4: Dilute the Muriatic Acid With Water in an Acid-Resistant Container

Your water to muriatic acid ratio should be 10:1, and remember – always add water to the bucket first and then pour the muriatic acid. If you pour the acid in first, you risk a chemical reaction.

Step 5: Keep Baking Soda Nearby, As Well as a Hose of Water

Baking soda is a perfect alkaline substance to neutralize the acid or quickly remove it from your skin. As an extra tip, be sure to store the acid as indicated and follow instructions on your local recycling center for disposal.

Step 6: Follow the Directions on the Test Kit

The instructions on the kit will explain that you should start with a small dose and pour slowly to avoid spills or splashes that could throw the numbers off.

Step 7: Make Sure the Pump and Filter Stay Running During This Process

After applying the recommended dose, leave the pool water alone for at least two hours to circulate.

Step 8: Retest the ALK and pH Again

Add more muriatic acid if the numbers are still off to reach the proper alkalinity levels. You can add slightly more while aerating so the pH rises to normal levels. Remember that while muriatic acid will lower the total alkalinity and pH levels, they may decrease at different rates.

Step 9: Adjust pH Accordingly and Return to Normal

If the pH levels don’t go back to normal (7.2-7.6) in a few days, add small amounts of sodium carbonate for a manual increase.

Don’t lower the pH to the lowest value on the kit since this will deplete your pool pH levels. Make sure the pH is slightly higher than the lowest pH value, and try not to lower the pH all at once. Apply gradually, in stages, for accuracy.

Here’s a YouTube video that does a good job explaining how to correctly add muriatic acid to your swimming pool.

Step-by-Step: How to Safely Clean Your Cartridge Filter With Muriatic Acid

Here is my handy step-by-step guide for cleaning your filter with muriatic acid.

Step 1: Turn Off the Filter

First things first, you need to turn off the filtration system. Take extra care to turn off any timers as well that may restart the filter while you are cleaning it.

Step 2: Open the Air Relief Valve

Get all the air out of the filter by opening the air relief valve. Doing this will also drain out the extra water from the filter.

Step 3: Remove the Cartridge

To clean the filter, remove the cartridge from the unit. To do so, check the manufacturer’s instructions.

Step 4: Soak the Filter in Muriatic Acid

Fill a big bucket or a trash can with one part muriatic acid and twenty parts water. Make sure to add the muriatic acid to the water, and not the other way around! Then put the filter into the mixture and let it soak until the bubbling stops.

Step 5: Rinse the Filter

Rinse the filter to ensure no more muriatic acid is left on the cartridge.

Step 6: Replacis e the Filter

Put the cartridge filter back into the unit and restart your filter!

How to Safely Clean Your DE Filter With Muriatic Acid

You can also use muriatic acid to clean your DE filter. Cleaning a DE filter is a bit more complicated, so if you need to do this, check out my complete guide on cleaning and backwashing a DE filter.

Is Muriatic Acid Safe to Use?

Muriatic acid is absolutely safe to use – if you take the proper precautions. Since it is an acid, you must wear safety gear and cover up your skin. Wear long sleeves, pants, closed-toe shoes, gloves, goggles, and even a respirator or mask. Once you’ve covered up, you should also ensure that you always add muriatic acid to the water, and not the other way around, as this can cause a chemical reaction. And take care to never mix muriatic acid with other chemicals. Storing muriatic acid properly is another important safety tip to keep in mind.

Get My Free Pool Care Checklist

Download my free, printable pool maintenance checklist to help you accomplish regular pool care tasks for any type of swimming pool.

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Frequently Asked Questions

How Much Muriatic Acid Do You Put in a Pool?

The amount of muriatic acid you will need to add to your pool depends on the pH level and the gallons of water your pool can hold. My pool alkalinity calculator is a great tool for finding this amount.

Can You Pour Muriatic Acid Directly Into Your Pool?

Pouring muriatic acid directly into your pool can be dangerous because it will not be diluted. Doing this, you risk damaging concrete or pouring it on yourself. Just remember to fill the bucket with water before adding the acid. If you don’t, it can cause a chemical reaction. And you should always wait before swimming after adding muriatic acid to your pool.

Can Muriatic Acid Damage Your Pool?

Adding too much muriatic acid will lower the pH levels. If the pH drops too low, it can damage your pool equipment and even cause rashes or burns to anyone who swims in the pool.

When Should You Use Muriatic Acid In Your Pool?

Muriatic acid lowers the alkalinity of the pool. So if the pH levels are measuring above 7.8, it may be time to add some muriatic acid.

Muriatic Acid vs. Hydrochloric Acid vs. Sulfuric Acid: What’s the Difference?

Muriatic acid and hydrochloric acid are actually the same chemical compound. The main difference between the two is that muriatic acid is less pure because it is diluted (around 20 percent). Sulfuric acid is a different chemical compound altogether that contains sulfur (you can read my entire article on using sulfuric acid in your pool if you’re curious). Conversely, hydrochloric and muriatic acid contain chlorine.

Muriatic acid is also different from dry acid. I cover the major differences (and use cases) in my complete research on dry acid vs. muriatic acid.

Final Thoughts

Adjusting alkaline and pH levels is not easy at first, but it is a learning experience that will protect you and your pool investment for the long term. Follow the testing kit directions closely, and you will get the hang of it! If you’re uneasy about the safe handling of muriatic acid, try sodium bisulfate, which is a bit slower to take effect, but can still get the job done.

If you need to raise your pool alkalinity instead, read my complete guide on raising your pool alkalinity.

Curious to learn more about the proper chemical levels for your pool? Be sure to read my guides on pool water chemistry 101 and the order to add pool chemicals as well. If you’re curious about learning how to use muriatic acid to clean your pool, read my guide on how to acid wash your pool.

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