How to Add Muriatic Acid in Your Pool to Lower The Alkalinity

Alkalinity plays an important role in pool cleaning. Too high a value should not be underestimated and leads to cloudy water.

But how can you lower the alkalinity with Muriatic acid?

In this article, I will show you how to properly use muriatic acid in the pool to lower alkalinity.

What does muriatic acid in swimming pools?

The acid in muriatic acid is hydrochloric (a form of hydrogen chloride gas). It lowers the alkalinity of swimming pools by reacting with calcium carbonate, making them less basic and more acidic. This will help you lower the alkalinity and pH levels in your pool water.

It is most often used for household cleaning, where it helps dissolve grime, stains, and buildup from common surfaces in kitchens and bathrooms.

But you can use a special muriatic acid for swimming pools to lower the alkalinity.

You just have to be sure that you use it with safety precautions.

Muriatic acid is a dangerous substance that can cause severe chemical burns on the skin and the eyes, making it one of the most hazardous acids to handle.

Tip: Read my blog post about what is alkalinity and what does it do?

Why is too high alkalinity bad in pool water?

Pool alkalinity is the measurement of the carbonates and bicarbonates in your swimming pool water. It’s a key factor when it comes to maintaining a healthy swimming pool.

The alkalinity in the pool water is too high when it exceeds the maximum allowable limit of 120 ppm. This causes the pH to climb higher than 7.6, making your sanitizer less effective.

Too high alkalinity can cause staining, cloudy water or white deposits on metal surfaces, while too low alkalinity can lead to poor sanitization and the growth of bacteria or algae.

The best way to lower the alkalinity is to use sodium bisulfate (dry acid). I show you how to lower the alkalinity with muriatic acid in this post.

Note: Alkalinity and pH are directly related. Higher alkalinity causes a higher pH level. When we optimize the alkalinity and the pH in the pool, we have first to balance the alkalinity and afterward the pH level.

Okay, let’s get started on how to lower the alkalinity with muriatic acid in your pool.

How to lower the pool alkalinity with muriatic acid?

The ideal alkalinity in a pool should be between 80 – 120 ppm (mg/l). Everything above is bad for your health.

Seriously. When you have alkalinity in the ranges as mentioned above, your bathers will feel much better, the risk of any kind of itching will decrease significantly, and so on.

When it comes to lowering the pool alkalinity, there are several ways to do this. Today we are going to use muriatic acid.

Supplies you will need:

  • One gallon of muriatic acid (hydrochloric acid).
  • Test kit for pool chemicals (a simple test kit should work fine).
  • Rubber gloves, safety glasses, and older clothes you don’t care about getting ruined.

Don’t let your pool get too alkaline.

Here’s how to use muriatic acid to lower your swimming pool’s alkalinity and keep it healthy. This easy step by step guide shows you how much acid you need and how to dilute it so that you can get the perfect pH level for your pool.

  1. First, take care of your safety and put some rubber gloves on. If you don’t have safety glasses, at least use your sunglasses.
  2. Test the pool water and calculate how much acid you need to lower the alkalinity. You can measure the alkalinity level with a test kit or use an electronic one.
  3. Then, take a bucket and fill it with pool water. Pour the amount of muriatic acid into the bucket.
  4. Start the pool pump and then add the acid slowly to the water and stir it well. You can avoid acid splashes by adding the liquid into the return nozzle of your pool.
  5. Let the pool pump run for at least half an hour before you retest the water.
  6. When the alkalinity is between 80 to 120 ppm, you can start optimizing your pH level.

The perfect time to start this process is early, when nobody enters the pool.

I always recommend wearing old clothes, because it always can happen that some acid splashes ruin the clothes.

You are not sure how much muriatic acid you need to add to be effective?

You need to add about 1 lbs. of acid per 10,000 gallons (3785 liters) to lower alkalinity by about 5 ppm.

You should test your pool water after adding this amount because it may take more or less muriatic acid depending on the starting pH before you add it and how much calcium is in your water.

If you have a lot of evaporation, high TA, and low pH, it may take more acid to lower alkalinity. If you have less evaporation, low TA, and high pH, it may take less muriatic acid to lower alkalinity.

Don’t worry about the pH level. It is normal to drop because we add acid into the pool. After you balance the alkalinity, it is much easier to optimize the pH.

Tip: If the alkalinity level has been lowered too much, then read my article on how to increase the alkalinity in the pool.

Aerate your pool to bring back the pH

When you balance the alkalinity in your pool, it is always recommended to aerate your pool to bring back the pH level to an optimum at 7.2 – 7.6.

The pool circulation is a natural way to raise the pH level of your pool because it brings back the carbon dioxide that has been removed during chemical treatment.

The more surface water that enters the pump, the higher the chances of this increase in pH.

Turn on your pool pump to aerate the water, or use a pool fountain to improve the water circulation.

Retest the alkalinity in the pool water

Okay, you lowered the alkalinity in your pool with muriatic acid and brought back the pH level.

You need to retest the pool water the last time to ensure that your water is balanced.

Everything is fine when the alkalinity is between 80 – 120 ppm, and the pH level is between 7.2 and 7.6. Otherwise, you have to start again with my described steps above.

Also, make sure that your other sanitizer levels like chlorine and bromine are within the right levels.

Repeat the process of lowering the alkalinity with muriatic acid

It is not unusual to repeat the process of lowering the alkalinity in your pool.

If necessary, you must test the pool water and add more muriatic acid in small doses. Repeat as many times as necessary to lower the alkalinity.

Once you achieve the appropriate alkalinity level, test it with regular pool water test strips every couple of weeks. Especially the first two weeks are important to check the alkalinity and the pH level in your pool.

The last tip.

When you can’t lower the alkalinity in your pool, maybe your measurement method is not suitable.

Test strips are inaccurate, and I always recommend using an electronic water tester.

Alternatively, you can bring a small water sample to a pool store where they are equipped with the right tools.

Do you have further questions about using muriatic acid in your pool?

The best way to contact me is @contactswimfool on Twitter or Pinterest. I am happy to help you.

Have fun swimming!

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Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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