Lowering Pool Alkalinity

How to decrease total alkalinity in your swimming pool

Do you have cloudy pool water?  The occasional plugged filter and scaling on equipment surfaces?  How about higher water pressure reading on your pool pump or sand filter even though you have backwashed?  These are all symptoms of high swimming pool water alkalinity.

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In this article, I explain how to decrease the alkalinity level in your pool water.  You can get an overview of how to manage your swimming pool alkalinity by reading my other article: Maintaining Swimming Pool Alkalinity.  You can also learn how to test alkalinity: Testing Swimming Pool Alkalinity, and raise the level if it is too low: Raising Swimming Pool Alkalinity.

Importance for your pool

Why lower the pool water alkalinity level?

Although high total alkalinity is not as severe to your pool surfaces and equipment as low alkalinity, the alkalinity level still needs to be maintained to prevent potential unplanned maintenance costs resulting from damage and wear to pool equipment, such as a pool pump motor life being cut short due to plugged filters and reduced pipe flow from scale buildup.

Swimmers will often experience irritation while swimming in a pool with high alkalinity.  Skin and hair will feel sticky, and their eyes might burn.

The pH level is harder to control in a pool with high alkalinity, as the buffering ability of the water to resist changes in acidity is so high, that attempting to adjust the pH requires greater amounts of chemicals.

I discuss more problems that can happen if your alkalinity is high for an extended period of time in my other article:

Keeping your total alkalinity balanced is an essential step to keeping your pool water healthy.  Balancing total alkalinity is one of three adjustments you do to balance your swimming pool water.  The other two are pH and calcium hardness.

You should always adjust total alkalinity first, except when pH is far below 7.0. Get pH to at least 7.0 first before adjusting total alkalinity.

Why is my total alkalinity level too high?

You may have added too much sodium bicarbonate, also known as baking soda, when increasing your total alkalinity.  You may want to add only a portion of the chemical required to adjust your water and wait between  six hours and 24 hours before testing the level.  Adding chemicals in smaller increments can help prevent adding too much.

The local water source may be the cause of high alkalinity, as municipal water sources lean toward a higher alkaline water level to prevent corrosion in pipes and sewer lines.  So, your local water source may be slightly alkaline.  A call to the municipal water company, details on their website, or perhaps you receive a yearly brochure detailing the water quality levels.  Knowing this will help during testing and reducing the level, as you might expect the alkalinity to rise on its own as you replace lost water through swimming, splashing, backwashing, and evaporation.

How to Lower Swimming Pool Alkalinity

Make sure to know the size of your pool, specifically the volume, as this value is required to know how much chemical to add to your swimming pool.  As for the total alkalinity range, you ideally want to be in the middle of the range: 80-120 ppm (parts-per-million).

There are two main chemicals available to lower alkalinity: sodium bisulfate, also known as dry acid, and muriatic acid.

Decrease total alkalinity with sodium bisulfate (dry acid).

Sodium bisulfate dry acid swimming pool alkalinity reducer

Sodium bisulfate, also called dry acid, can be used to reduce pool water total alkalinity.

  1. Test the swimming pool total alkalinity level.Make sure you have tested your pool total alkalinity.
  2. Turn the swimming pool pump off.Turn the pool pump off and wait one hour to let the pool circulation stop.
  3. Read the product label.If your level is above 120 ppm, then you need to lower the level to about 100 ppm. Read the label on the back of the product package to determine how much to add.  Sodium bisulfate is typically 93.2% pure, so make sure you find this percentage on the package.
  4. Dilute.Dilute the dry acid in a bucket of water. Make sure the substance is completely dissolved.
  5. Add to the pool water.At the deep end of the pool, pour the diluted dry acid into the water, making sure to keep the stream as narrow as possible.  You want the stream to penetrate the upper area of water and get as deep as possible.  This helps to avoid disrupting the pH level in the water.
  6. Let the pool sit.Leave the pool to stand still for one hour.  After one hour turn the pool pump back on.
  7. Test the pool water.Retest the total alkalinity level after six hours, but before 24 hours after you have added the dry acid mixture.
  8. Repeat if necessary.Dilute and add more dry acid if you need to bring your level down a little more, but wait at two to three days before adding more, as the total alkalinity may still drop somewhat.

Lowering total alkalinity with Muriatic Acid

muriatic acid swimming pool alkalinity reducer

Muriatic acid, used to reduce the pH in swimming pools.  Don’t spill it on concrete!

Caution: Muriatic acid is slightly diluted hydrochloric acid.  This acid will burn eyes and skin, so you need goggles, rubber gloves, and should wear a long sleeve shirt when working with this substance.

  1. Test the swimming pool total alkalinity level.You need to know if the level is high, and by how much.
  2. Turn the swimming pool pump off.Wait one hour for the water to stop circulating in the pool, as you want the water to be as still as possible.
  3. Read the product label.Determine how much to add, based on the amount your level is over (in ppm), and the volume of your swimming pool.
  4. Dilute or add directly.You can either dilute the muriatic acid, or pour the acid in directly to the water.  Make sure to do this in the deep end of you have a diving pool, or pour a portion in several spots if you have a shallow or sport pool.  Keep the stream tight, as you want the liquid to flow towards the bottom of the pool.
  5. Let the pool sit.Leave the pool alone for about one hour, and then turn the pool pump back on.
  6. Test the pool water.Test the total alkalinity between six and 24 hours after adding the chemical to give the pool a chance to adjust to the muriatic acid you have added.
  7. Repeat if necessary.You may need to add more muriatic acid if the level has not dropped enough, but wait two to three more days before adding any more, as total alkalinity sometimes takes several days to re-balance.
  8. Check the water pH.Your pH may have dropped as well.  Be sure to test the pool pH and adjust pH up if necessary.
Tips on lowering swimming pool total alkalinity

  • I also have instructions for using dry acid and muriatic acid in another article: Lowering Swimming Pool pH.  The instructions are similar, so be sure to follow the instructions for lowering alkalinity if it is your total alkalinity that needs to be lowered.  The primary difference between the two instructions is you want to avoid lowering the pH when lowering total alkalinity.
  • Both of the products described above might be labeled with names like Alkalinity Decreaser and Alkalinity Minus.
  • Add half to three quarters of the amount suggested.  Make sure it is dissolved and retest alkalinity several hours later.  You want to avoid lowering alkalinity too much.  Determine how much remaining chemical to add to bring the total alkalinity back into the center of the range.
  • Even if you do your best to pour the liquids in the pool, you still will often end up lowering the pH level somewhat.  Test the pH when you adjust and test total alkalinity to make sure your pH has remained balanced, or if you need to raise the level somewhat.
  • After months and years of testing, you may notice patterns in your alkalinity, such as adding water tends to raise or lower alkalinity.  You may want to adjust the amount of alkalinity reducer you add to the water based on this knowledge that your water alkalinity will tend to wander up or down.

Conclusion

Keeping total alkalinity in balance is one of the important three water balancing steps.  You need to know how to test your total alkalinity, and how to lower the level if it is too high.  You also need to know which chemicals are available to lower total alkalinity, and how much to add based on your pool size and how much you are over.

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Source:

  • “Pool & Spa Water Chemistry, A Testing and Treatment Guide, Waterproof Edition, 2005. Taylor”

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