What is sodium bisulfate for pools?

 Are you familiar with the names pH down, pH decreaser or dry acid which are known to lower the pH as well as the total alkalinity of your pool?  If your answer is yes, then somehow, you’ll have an idea as to what is sodium bisulfate for pools.

Sodium bisulfate is dry acid

sodium bisulphate

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In case you haven’t known yet sodium bisulfate and dry acid are practically the same substance. Sodium bisulfate which results from the mixture of sulfuric acid and sodium hydroxide is the chemical name of dry acid.

It is usually processed into white granules that are added into the pool with high pH and alkalinity. Sodium bisulfate lowers both the pH and total alkalinity, thus help maintain the water balance of your pool.

Dry acid vs. Muriatic acid

Aside from dry acid, muriatic acid (hydrochloric acid is also effective in lowering the pH and alkalinity of pools. However, dry acid is more  preferred because  it is more easy to use and being  less corrosive  won’t cause burns or damage pool surfaces easily in case of accidental spillage.

It is also easy to store, although just like any acid requires proper handling and care.

How to lower pH with sodium bisulfate

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Ensuring your pool water pH at its optimum level is a critical part of pool maintenance since it makes your pool safe by enhancing the effectiveness of chlorine in your pool.

If you experience skin and eye irritations, or if your scalp itches after swimming, and your water looks cloudy or you notice mineral deposits  around the pool area, it is most probable that your pH is too high and needs to be lowered.

In The Swim Pool pH Reducer is 93.2% sodium bisulfate in granular form that is safer and easier to store than muriatic acid. Get it here.

Let’s go through the step-by-step guide below:

  • Read the label of the product. Different manufacturers have different percentages of sodium bisulfate in their products, the common being 93.2%.
  • Test the pH level of your pool. The first step is to test your pool pH level to determine how high it may be, and by how much. If the pH level is above the ideal range (7.2-7.6) then you need to adjust and lower your pH to 7.4 to be at its optimum.
  • Determine how much sodium bisulfate to add. The amount of acid will depend on your test results. It is recommended to add ¾ of the required amount and add more later if the pH level is still high. This is to avoid adding too much and end up having to raise the pH.
  • Dilute if necessary. If in case the instruction says to dilute, and then follow product instructions on how to dilute. This way you can balance both the pH and alkalinity. Undiluted products may react with water faster which could result to the lowering of alkalinity instead, without any effect on the pH.
  • Add the dry acid to the pool. Dry acid usually comes in powder form, so take precaution when adding the amount into the pool so that it would not just be carried by the wind or land on your clothes or skin.

    Pour the acid into the return jet sights where the water flows through into the pool to ensure that it is spread evenly in your pool. Do not pour into the water near the inlet sights otherwise, the dry acid will just be pulled by the pump and drawn into the filter. In 5-15 minutes you should see the substance disappear since it is highly soluble in water.

    NOTE: For pools above ground, dump the dry acid along the wall of the pool. Since above ground pools are usually shallow, you may be required to manually spread the dry acid in the pool to make the powder dissolve quickly.
  • Allow the pool to sit. You should wait at least six hours before retesting, but do not wait for more than 24 hours after adding the last portion of the dry acid.
  • Retest and repeat steps if necessary. If upon retesting, you find the pH still high, then go through the steps again.

    NOTE: Sodium Bisulfate will lower your alkalinity as well as the pH, so retesting should be done for both.

How to lower alkalinity with sodium bisulfate

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Aside from maintaining the pH level of your pool, you must also check its alkalinity periodically. High alkalinity can irritate your eyes and make your skin dry and itchy.

It can also cause scaling and mineral deposits on the pool which can lead to staining of the floor and walls. Make sure to always maintain the proper alkalinity level, and you will have fewer problems with pH changes.

  • When lowering your alkalinity (just like in lowering the pH), you should read the product’s label to be sure that it contains 93.2% sodium bisulfate. Also, you should know the volume of your pool as this is required in determining how much sodium bisulfate should be added to the pool.
  • Test the pool total alkalinity. To determine how high your pool alkalinity may be, and by how much, test your pool alkalinity. The ideal range is 80-120ppm, if upon testing your total alkalinity is above120ppm, then you need to adjust and lower your alkalinity to 100 ppm.
  • Determine how much acid to add. The amount of sodium bisulfate will depend on your test results. It is recommended to add ¾ of the required amount and add more later if the alkalinity is still high. This is to avoid adding too much and end up having to raise your alkalinity.
  • Turn off the pool pump. Wait at least 1 hour for the pool circulation to stop completely before adding dry acid to your pool.
  • Dilute the dry acid. Dilute the amount of dry acid in a bucket of water, making sure that it is completely dissolved. Follow the manufacturer’s instructions on how to dilute.
  • Add to the Pool. Pour the diluted dry acid into the deep end of the pool, ensuring to keep the stream as narrow as possible. This makes the stream penetrate the upper area of the water and gets as deep as possible without disrupting the pool pH.

    Note: You should monitor the pH level of your pool while adding the acid.
  • Retest and repeat steps if necessary. Retest the total alkalinity after 6 hours, but not beyond 24 hours after you have added the diluted dry acid. D dilute and add more dry acid if you still need to bring the level down. If you need to repeat the treatment, do it after 2-3 days.


  • Extreme care must be taken when adding acid to the pool as it can cause serious burns. Ensure nobody is swimming or will use the pool before four hours are over.
  • Make sure to add acid to water, never add water to acid.
  • Don’t add large amounts of acid in the pool at one time. You may risk damaging the walls, corroding the pump fitting and pipe and end up having to raise the pH and alkalinity levels.

Sodium bisulfate is an essential substance in maintaining water balance of your pool. It is effective in lowering the pH and alkalinity of the pool. With sodium bisulfate, keeping your pool clean and safe is made easy.

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