Muriatic Acid vs Dry Acid: Which One Should You Use in a Pool?



Muriatic acid and dry acid are easily the most common acids for lowering pH and alkalinity in a swimming pool.

However, it’s not always clear which one you should use, and whether there are any significant upsides to using one over the other.

This article will settle the debate on muriatic acid vs dry acid, starting with the basics of each acid, and finishing with a clear comparison and overall winner for which one you should use.

What is Muriatic Acid?

CPDI Acid Blue Muriatic Acid Swimming Pool pH Reducer Balancer and Concrete...
CPDI Acid Blue Muriatic Acid Swimming Pool pH Reducer Balancer and Concrete...

    Muriatic acid, or hydrochloric acid, is a liquid acid that naturally occurs in the human body.

    This acid is also often commercially produced and sold in 1-gallon jugs as a household cleaning solution, specifically for cleaning stains and grout.

    Finally, and more importantly, it’s also used in swimming pools to quickly lower the pH and total alkalinity of the water, as well as acid washing pool plaster.

    Quick stats:

    • It comes in liquid form
    • It’s typically sold in 1-gallon jugs
    • It has a pH level of between 1 and 2
    • Available in 15% and 31% strengths

    What is Dry Acid?

    In The Swim pH Reducer for Swimming Pools, Spas, and Hot Tubs - Lowers...
    In The Swim pH Reducer for Swimming Pools, Spas, and Hot Tubs - Lowers...

      Dry acid, or sodium bisulfate, is a granular acid and a popular alternative to muriatic acid.

      It’s commercially produced and often sold by the bucket, where it’s used in a wide variety of cleaning products and other applications. For example, it’s also found in certain supplements as well as medicinal creams.

      Of course, it’s also used in pools to lower pH and alkalinity, and it’s just as effective as muriatic acid at doing so.

      Note: Sodium bisulfate is sometimes confused with sulfuric acid, and while the latter can also be used to lower a pool’s pH, it’s not the same substance.

      Quick stats:

      • It comes in granular form
      • It’s typically sold in bags or tubs
      • It has a pH level of 1
      • Only available in 93% strength (before dilution)

      Muriatic Acid vs Dry Acid (Differences)

      Both muriatic and dry acid reduce pH and alkalinity equally, so it can be easy to overlook their differences.

      These are the main differentiators:

      Muriatic Acid Doesn’t Add Sulfates to the Water

      Dry acid is sodium bisulfate, which means it contains sulfates.

      Typically, if your sulfate level is higher than 300ppm, your water will start to attack concrete pool surfaces, corrode metal components (including saltwater generators), and even weaken vinyl pool liners.

      As a general guide, you add almost 10 parts per million (ppm) of sulfates for every pound of dry acid you add to 10,000 gallons of pool water.

      While this might not sound like much, consider that adjusting pH from 8 to 7.6 requires roughly a pound of dry acid, so frequent or more drastic adjustments will quickly pile on the sulfates, and they’re notoriously difficult to remove.

      Muriatic acid doesn’t contain sulfate, so you can use it as much as you want without having to worry about monitoring the sulfate level in your pool.

      Muriatic Acid Doesn’t Need to be Pre-Dissolved

      Dry acid comes as solid granules.

      Considering how much stronger it is compared to muriatic acid (93% vs 15/31%), it’s not surprising you can’t just throw the granules directly into your pool water.

      Instead, dry acid needs to be added to a bucket of water in order to pre-dissolve before adding it to your pool. This will dilute the strength of the acid enough to prevent any damage to your pool surfaces.

      Muriatic acid comes in liquid form.

      While it can be diluted before adding to your pool, it certainly doesn’t need to be. With steady handling, you can pour muriatic acid directly into your pool water, saving several time-consuming steps in the process.

      Muriatic Acid is Slightly Cheaper than Dry Acid

      Whether you buy online, in a hardware store, or in your local pool store, muriatic acid will often come out a bit cheaper.

      The problem is, the difference in price is hard to gauge as it’s often difficult to compare a liquid acid vs granular acid, especially when they come in at vastly different strengths.

      Instead of measuring by weight or volume, it’s easier to compare the two by the cost of pH reduction.

      For example, using some pool math, we know going from a pH level of 7.9 to 7.5 requires roughly 12 oz (354ml) of 31% strength muriatic acid, or 16 oz (1 lb) of dry acid granules

      Using average online prices:

      • 354ml of muriatic acid equates to about $7 in cost (1 gallon at $20)
      • 1 lb of dry acid equates to about $9 in cost (2 lbs at $18)

      As you can see, muriatic comes out cheaper at smaller volumes. Price can sway in favor of dry acid at much higher volumes, however, since you can now buy 25 lb and 30 lb tubs for a heavily discounted price.

      Dry Acid is Arguably Easier to Handle

      Regardless of your strength or dexterity, solid granules are usually considered easier to handle than liquid.

      While the extra step of dissolving granules before adding them to the pool makes dry acid somewhat less efficient, transferring solid granules gives you a wider margin for error than transferring liquid.

      If you accidentally drop any granules, it’s not going to cause any immediate harm or damage, assuming you’re quick to pick it up. The same can’t be said for muriatic acid, which can eat away at your concrete or decking.

      We say “arguably” because, after the granules have been pre-dissolved, you still need to transport the bucket of dissolved acid to your pool water. This isn’t wildly different from just using muriatic acid.

      Dry Acid Doesn’t Give Off Dangerous Fumes

      One of the worst aspects of handling muriatic acid is accidentally breathing the dense fumes or vapors it gives off.

      If attempting to add muriatic acid to your water against the wind direction, the fumes can blow directly into your face. This can be particularly problematic if you’re not wearing a mask.

      Inhalation of muriatic acid fumes can lead to a number of immediate and long-term health issues, including coughing, choking, chest pain, and internal inflammation, though severe symptoms would require significant exposure. 

      Lower strength (15%) muriatic acid also mitigates the strength of the vapors and is often preferred by pool owners for this reason.

      Dry acid doesn’t pose the same risk, even after dissolving the acid granules in a bucket of water – at least not nearly to the same degree.

      Verdict: Use Muriatic Acid

      Despite a slightly steeper learning curve in terms of handling muriatic acid, it’s still the overall best option for pools when it comes to frequent use.

      The sulfate issue alone is enough to claim victory. Throw in the convenience of not having to pre-dissolve it and the fact that it’s often cheaper than dry acid, and you have yourself a clear winner.

      Categories: Pool Care, Pool Chemistry