What Does Sulfuric Acid Do to a Pool? (Should You Use It?)



You might come across sulfuric acid when you’re dealing with pool care, but exactly does this acid do for a pool?

We’re going to cover exactly what sulfuric acid is, why it’s used in swimming pools, the pros and cons of using it, and whether you should actually use it in your pool.

Short answer: Sulfuric acid is used to lower the pH level and total alkalinity of your pool water when it’s too high, though it does have a number of downsides that make alternatives like muriatic acid and dry acid better options overall.

What is Sulfuric Acid?

Sulfuric acid, or sulphuric acid, is most commonly used in fertilizers.

It’s also used in various other chemicals, such as in dyes and pigments, washing detergents, certain types of drugs, and even explosives.

Interestingly, sulfuric acid is one of the main ingredients of dry acid (sodium bisulfate), which is a granular, dissolvable type of acid that’s often used in swimming pools.

Sulfuric acid is sold is typically sold in 1-gallon jugs at only 38% strength, which is far weaker than dry acid at 93%.

Why is Sulfuric Acid Used in Pools?

Sulfuric acid can be used to increase the acidity of your pool water, and therefore lower its pH and total alkalinity.

It’s basically an alternative to muriatic acid or dry acid when used in pool chemistry, and it’s equally as effective at lowering both of these levels.

Like the alternatives, sulfuric acid can be used to target pH even though it will also impact alkalinity. In this case, sulfuric acid would later be paired with sodium bicarbonate (baking soda) to raise alkalinity back up in isolation.

Sulfuric acid isn’t nearly as popular, however, and there are a number of good reasons for why that is.

The Benefits of Using Sulfuric Acid

Let’s start with why you should use sulfuric acid in your pool.

It Doesn’t Give Off Harsh Fumes

Some acids are harder to handle than others, and that’s partly due to the fumes they give off.

In particular, muriatic acid gives off strong vapors that can lead to repository issues and internal swelling after long or repeated exposure. While this is only ever a concern under poor handling, it’s still something many pool owners prefer to avoid.

Both dry acid and sulfuric acid aren’t nearly as potent as muriatic acid in regards to fuming, and this similarity isn’t surprising given that sulfuric acid is used to make dry acid.

For anyone who doesn’t like the sound of potentially breathing toxic vapors while adjusting their pool chemistry, “fume-free” sulfuric acid sounds a lot more appealing.

It Doesn’t Need to be Pre-Dissolved

Sulfuric acid and dry acid are very similar (remember, sulphuric acid is an ingredient of dry acid).

Dry acid, however, comes in granular form, meaning it has to be pre-dissolved in a bucket before being added to a swimming pool.

While many pool specialists who use dry acid consider this a minor inconvenience, this additional step requires more equipment and slows down the process of reducing the pH and alkalinity of your pool water.

Like muriatic acid, sulfuric acid is a liquid acid. Both acids are diluted enough that they can be poured directly into your pool.

It’s Cheaper to Buy

Muriatic acid is often touted as the cheapest pool acid, but sulfuric acid is actually similarly priced, if not slightly cheaper.

For example, looking at the average online price:

  • 1-gallon of muriatic acid is between $10 and $15
  • 1-gallon of sulfuric acid is between $5 and $15

While it’s harder to compare the price against dry acid (sodium bisulfate) due to it being solid granules, it’s well-established that dry acid is often more expensive than both acid alternatives in terms of net effect.

With that being said, dry acid does become significantly cheaper at larger volumes, so buckets of 25 or 30 pounds may work out more cost-effective in the long run.

The Drawbacks of Using Sulfuric Acid

Now, here are all the reasons why you shouldn’t put sulfuric acid in your pool.

It Adds Sulfates to Your Water

Sulfate is a mineral salt that can be introduced to your water through the use of various pool chemicals.

Sulfuric acid, as the name suggests, is one of those chemicals.

Low levels of sulfate aren’t anything to worry about, but long-term use will compound the amount of sulfate in your water until it’s concentrated enough to become corrosive to your pool surfaces and equipment.

Most experts agree that over 300 parts per million (ppm) is the danger zone, and you can expect to add around 50 ppm of sulfate per gallon of sulfuric acid used, per 10,000 gallons of water.

The only way to counter a buildup of sulfates from sulfuric acid (or dry acid) is to frequently drain or partially drain your pool. If you happen to be doing that anyway, for whatever reason, sulfates are likely a non-issue.

Muriatic acid is the only acid of the three that doesn’t contain sulfate, which is the main reason it’s often recommended over the alternatives.

It’s More Dangerous to Handle

When you’re dealing with liquid anything, spillages are all but guaranteed.

Spilling acid in or around your pool is never ideal, especially because it can have lasting damage to your pool deck or coping. It’s also very corrosive to concrete and plaster.

At 38% strength, sulfuric acid is highly concentrated, and certainly more caustic than its close cousin; sodium bisulfate (dry acid). Improper handling could result in burning of the skin or hair.

These risks are still present when using both dry acid and muriatic acid in your pool but to a lesser degree. 

It’s Harder to Find in Most States

For all its benefits, sulfuric acid isn’t nearly as popular as dry acid and muriatic acid.

In fact, finding it locally can be difficult unless you reside in Florida, which appears to be the only state where sulfuric acid is preferred.

Even online listings for sulfuric acid are scarce, so if you are leaning toward using this pool acid, nailing down a regular supply could be near impossible depending on where you live.

Bottom Line: Don’t Use Sulfuric Acid

Despite some obvious upsides to using sulfuric acid in a pool, the buildup of sulfates is reason enough to rule it out as a viable pH and alkalinity reducer, at least for prolonged use – and the same goes for dry acid.

Instead, use muriatic acid. It shares almost all of the same benefits as sulfuric acid without littering your water with sulfates, and aside from a slight learning curve when it comes to proper handling, it’s easily the superior pool acid.

Categories: Pool Care, Pool Chemistry