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  • Writer's picturePool Protection Technologies

Muriatic Acid: What Is It?

Updated: Jun 12, 2023

Maintaining a clean and balanced swimming pool requires diligent attention to water chemistry. One essential chemical that pool owners often turn to is muriatic acid (HCl), also known as hydrochloric acid. This powerful and corrosive acid serves multiple purposes in pool maintenance, including pH control, alkalinity adjustment, filter cleaning, and stain removal. However, it is crucial to handle muriatic acid with caution due to its potential hazards. In this comprehensive guide, we will explore the uses of muriatic acid in pools, its safety considerations, and step-by-step instructions on how to effectively use it for pH and alkalinity adjustment.


Muriatic Acid


Muriatic acid is a strong and highly corrosive acid commonly utilized in swimming pool maintenance. With a pH of less than 1.0, it is over a million times more acidic than neutral water. Pool-grade muriatic acid is similar to the hydrochloric acid used for cleaning concrete and brick, but it has a lower concentration of hydrogen chloride. Despite its effectiveness and affordability, it should be handled with care due to its potential dangers to the skin, eyes, and respiratory system.


Uses of Muriatic Acid in Pool Maintenance

  1. Lowers Total Alkalinity and pH: One of the primary uses of muriatic acid in pool maintenance is to balance water chemistry by reducing total alkalinity and pH levels. Total alkalinity acts as a buffer for pH, preventing rapid fluctuations. However, high alkalinity and pH can lead to issues such as cloudy water, reduced chlorine effectiveness, scaling, and potential damage to the filtration system. By carefully adding muriatic acid, pool owners can lower both alkalinity and pH levels, bringing them into the recommended range of 100-150 ppm for alkalinity and 7.4-7.6 for pH.

  2. Cleans Cartridge Filters and D.E. Grids: Pool owners who utilize cartridge filters or diatomaceous earth (D.E.) filters can benefit from muriatic acid's cleaning properties. Over time, filters accumulate debris and residue that can hinder their effectiveness. Muriatic acid can be used to deep clean cartridge filters, breaking down the accumulated residue and enhancing their performance. It is also effective in cleaning calcium scale deposits from D.E. filter grids, ensuring proper filtration.

  3. Removes Concrete Pool Surface Stains: Muriatic acid serves as a potent stain remover, particularly for concrete pool surfaces. It can effectively eliminate rust stains, restore the appearance of the pool deck and clean grout between swimming pool tiles. However, caution should be exercised when using muriatic acid on pool surfaces to avoid unnecessary corrosion or discoloration. It is advisable to test the acid on a small area before applying it extensively.


Safety Considerations


While muriatic acid is a valuable tool for pool maintenance, it should be handled with the utmost care. Here are some important safety measures to follow:

  1. Personal Protection: Always wear appropriate safety gear, including a respirator, acid-resistant gloves, eye protection, and fully-covering clothing. These precautions are necessary to protect your skin, lungs, and eyes from potential harm caused by the acid or its fumes.

  2. Dilution: For safe application, muriatic acid should be diluted in water. Add the acid slowly and carefully to a bucket that is already filled with water. Never add water to acid, as it can cause the acid to splash back. It is essential to use an acid-resistant plastic container for this process.

  3. Storage and Handling: Store muriatic acid in its original container and keep it away from other acids and pool chemicals. Mixing different chemicals can lead to chemical reactions or even explosions. Ensure that the container is tightly sealed and stored in a cool, dry place, out of reach of children and pets.

  4. Ventilation: Always work in a well-ventilated area to prevent the buildup of acid fumes. Open windows and doors, or use fans to promote air circulation. If working indoors, ensure proper ventilation systems are in place.

  5. First Aid: In case of accidental contact with muriatic acid, rinse the affected area with plenty of water immediately. Have a water source readily available for rinsing. If acid comes into contact with the eyes, flush them with water for at least 15 minutes and seek medical attention promptly. If swallowed or inhaled, seek immediate medical assistance.


Using Muriatic Acid for pH and Alkalinity Adjustment


To adjust pH and alkalinity levels, follow these step-by-step instructions:

  1. Test the Water: Before adding any chemicals, test the pool water using a reliable test kit to determine the current pH and alkalinity levels.

  2. Calculate the Required Amount: Refer to the product instructions or consult the Pool Protection Technologies Muriatic Acid Sheet to calculate the amount of muriatic acid needed to adjust the pH and alkalinity. Keep in mind that it is better to make small adjustments and retest than to overshoot the target levels.

  3. Dilute the Acid: Using an acid-resistant plastic container, fill it with water first and then slowly add the muriatic acid. Always add acid to water, not the other way around. Stir the mixture gently until fully dissolved.

  4. Application: For small adjustments, pour the diluted acid mixture directly into the pool's deep end. Alternatively, for larger adjustments, pour the diluted acid mixture into the pool while the pool pump is running. This will help distribute the acid evenly.

  5. Circulate and Retest: Run the pool pump for at least five hours to ensure thorough circulation of the treated water. Afterward, retest the water to verify the pH and alkalinity levels. If further adjustments are necessary, repeat the process.




What happens if I put too much muriatic acid in the pool?


Adding too much muriatic acid can drop your pH levels too low. Low pH can cause eye irritation and skin rashes. It can also erode metals like pool ladders, railings, nuts and bolts, and other pool equipment.


If you accidentally add too much muriatic acid and your pH levels have dropped too low, you can raise them back up with soda ash or pH increaser. And if you haven’t added your muriatic acid yet, go slowly. You can always add more later after you retest your water.


When can I swim after adding muriatic acid?


To be safe, wait at least an hour for the muriatic acid to dissipate, then retest your pool water before swimming again to make sure your pH isn’t too low. Adding muriatic acid directly to your pool can create an “acid hot spot” in the water. This can burn or irritate your skin, eyes, nose, and throat if you swim too early. The longer you wait, the safer it is.



Muriatic acid is a valuable tool for maintaining proper water chemistry in swimming pools. By understanding its uses, safety considerations, and proper application techniques, pool owners can effectively balance pH and alkalinity levels, clean filters, and remove stains. Remember, the key to using muriatic acid safely lies in careful handling, appropriate protective gear, proper dilution, and adequate ventilation. By following these guidelines, you can enjoy a well-maintained and sparkling pool all season long.


If you need to purchase muriatic acid, you can visit our online shop, where we have all the necessary pool chemicals to keep your pool up and running!



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