Last Updated: December 26, 2021

What Does Muriatic Acid Do For A Pool?

Written By: Pool Care Guide

Maintaining good water chemistry is essential for your swimming pool. To make sure that the pH of your water is in the sweet spot, you should be testing your water routinely. And sometimes, after testing, it might be a good idea to add muriatic acid to balance the water, ensuring it isn’t too alkaline. 

If that sounds complicated, we’re here to help. Our many years of pool service expertise have taught us what to do and what not to do. So, we’ll show you why you need to add muriatic acid and when, how to do it safely, and what to expect when you do.  

What Is Muriatic Acid?

Muriatic acid is a diluted form of hydrochloric acid. You can find it in most big box stores, often alongside the concrete cleaning products. It’s often near products like brick cleaner on the shelves because it is an excellent product for cleaning surface contamination off of natural stone and concrete. 

You can also find it in a smaller hardware store or even online. Swimming pool stores usually sell their own overly expensive balancing chemicals. They’re usually unnecessary and mostly a waste of your hard-earned money. 

When you find muriatic acid in the store, note that it comes in a heavy plastic jug. Ensure the jug’s not leaking and handle it carefully, as the acid inside is caustic and could damage your clothes or create fumes if it spills unintentionally. 

When to Add Muriatic Acid to Your Pool

So, why the heck would you want to add caustic acid to your swimming pool water? Well, when the water in your pool has become too alkaline, you need to use an acid to bring the water back toward neutral. Let us explain why. 

Most swimming pools need to maintain a specific pH value. You’re usually going to be looking for a pH reading of around 7.6 to 7.8 on your test kit or test strips.

When the water becomes too basic (or alkaline), you need to use a chemical to bring the water back to where it needs to be in terms of pH. If you don’t, the water could actually start to burn your eyes. And, if left too basic for too long, you could easily end up with problems like calcium buildup, scaling, and unpleasantly cloudy water.  

Note that some swimming pools require a slightly lower pH. For instance, pools that use a salt cell to produce chlorine require a pH of around 7.4 because salt systems tend to force the pH to creep up a bit. 

Some people become tempted to let nature try to control their pool’s pH. For instance, if your pool gets inundated with a downpour’s worth of slightly acid rain, you might not even need to add any chemicals. But that’s mostly wishful thinking. 

If you want to control your pool water the right way and not pray for rain to solve easy chemistry issues in your water, get a couple of jugs of muriatic acid and keep them on hand in a safe location. 

How Much Muriatic Acid to Add to the Pool 

Let’s assume you’re poolside with your handy pH test strips. You just followed the instructions and obtained a reading of 8.0, indicating that your water is way too alkaline. It’s time to use some muriatic acid to neutralize your water.

Now, using the amount of water in your pool, also called volume, you can calculate how much muriatic acid to add. Your test strips may have a handy reference to help you figure out what quantity you need to add to the water to find the right balance, or you can find one online. 

How to Add Muriatic Acid to Your Pool 

Adding muriatic acid isn’t something to be afraid of, but it is something that you should do carefully. So, follow a few safety tips:

  • Always open the jug in a well-ventilated space
  • Consider using safety goggles, gloves, a safety apron
  • Dilute the muriatic acid to a ratio of 5 parts water to one part acid in a bucket pre-filled with water
  • Turn your head away from the spout of the jug when open
  • Do not directly inhale any gas that escapes from the jug

There are two schools of thought about adding muriatic acid. Some pool guys say to shut the filter pump off before adding the acid. We are not in that school, and here’s why. 

When the filter is off, the acid will diffuse into the water but won’t circulate. It may develop a strong enough concentration to damage or discolor your pool’s liner, plaster, or other surfaces and equipment. So, here’s what we recommend instead. 

Leave the filter running, and add the muriatic slowly, or even in small doses, in front of the return plumbing to the pool, in the deep end, if possible. Your filter may even have a ‘recirculate’ mode, so you can bypass the filter and just keep the pump moving the water. 

By distributing the muriatic acid slowly, perhaps in a  few small doses, right in front of the jet of water in your pool, you’ll avoid creating a concentrated super-dose of acid that could damage your equipment.

It’s a good idea to also predilute the acid a little bit. So instead of pouring it directly from the jug, consider filling a bucket partway with water and then adding the amount of acid you need to the bucket as well. This will further minimize the risks of damaging anything with too strong a concentration of acid. 

Don’t ever add the acid to the bucket first, or the acid could react with the bucket and damage it or even leak through it.

After Adding Muriatic Acid to the Water

Once the acid is in the water, make sure to keep the water circulating. You can enhance the circulation by giving the sides and floor of the pool a nice brushing if you’d like, as this will mix the water even more. 

In about an hour, depending on the circulation speed of your filter and the size of your pool, the acid will have mixed with the water sufficiently to retest. If you are still too alkaline, add a bit more acid. 

When Will It Be Safe to Swim Again?

Muriatic acid is a diluted form of a powerful chemical called hydrochloric acid. The more powerful acid has been diluted to a concentration of about 30%, making it relatively safe to handle. 

But, it can still irritate your respiratory tract, cause temporary burning of the eyes and mucus membranes, and even cause severe inflammation if it or its fumes come into direct contact with your skin, eyes, or breathing passages. 

So, it’s a good rule of thumb to wait at least a couple of hours to swim after you add a dose of acid. But that might also be a bit overly cautious, especially for experienced pool owners or professional service persons. Again, you can use a swimming pool calculator to determine when the water is safe to swim in after adding chemicals. 

Our rule is that if the water is circulating well and also testing appropriately, the water is safe to swim for adults. Whenever there are kids going swimming, we recommend extending the buffer a bit and letting the water circulate until you’re 100% sure the acid has been thoroughly circulated, and there aren’t any overly-concentrated pockets left in the water. 

The biggest thing to remember about adding chemicals to your pool is that less is almost always best. You’d much rather have to add two or even three doses instead of overdosing the pool and having to add more chemicals to counteract the mistake you made. You could even end up in a situation where you’ll have to drain and refill the pool if you add chemicals too cavalierly. 

Are There Substitutes to Use Instead of Muriatic Acid?

You’re not going to find a more affordable chemical than muriatic acid to lower the pH in your pool. However, you can buy a chemical called sodium bisulfate in crystal form. It costs much more, but it is more stable and easier to handle. In addition to its higher cost than muriatic acid, the downside is that it takes at least a day to dissolve throughout the water completely.

If you’re really tuned into your pool’s chemistry, you may be able to avoid letting the pH creep toward alkaline. That means you won’t have to adjust the pH at all, at least not on a regular basis. That’s because many of the common sanitizers and algaecides we use in swimming pools already contain acids. 

  • Algaecides may increase the acidity of your pool when added to the water
  • Dichlor tablets contain chlorine sanitizers with a pH as low as 6.8
  • Trichlor tablets contain both cyanuric acid (chlorine stabilizer) and have a pH of 3.0 or lower


So, if you’re on a regular dosing schedule that uses any of these chemicals to control algae or sanitize the water, you might be able to also use them to balance the pH in your pool. Just keep in mind that you should have balancing chemicals on hand as well, as these others won’t get the job done if things are headed off the rails. 

Muriatic Acid: Safe and Effective

If you’re new to caring for a swimming pool, don’t be nervous about using muriatic acid. If you are careful and you follow the instructions here, everything will be fine, and you’ll be back swimming in no time. 

Get the chemicals you need now, so you’re prepared for balancing and treating your pool water all season long.

Frequently Asked Questions

How often should you put muriatic acid in your pool?

There isn’t a one size fits all for this question because the answer will vary too greatly due to local conditions. First, the acidity of rainfall will be dramatically different from place to place. Second, if your pool has waterfalls or sprinklers, it will cause the pH to continually rise. Third, if your alkalinity levels are too high, it might also cause the pH to continually rise.

What happens if you put too much muriatic acid in your pool?

Muriatic acid will lower the pH of your pool. If too low, it will deteriorate the pool. The surface will become rough and pitted, and the grout will erode. Healthwise, low pH causes headaches, rashes, and eye and skin irritation.

Can you pour muriatic acid directly into the pool?

You can, but it is not recommended. You should dilute it first and add that♡ diluted mixture throughout the pool. This will prevent too much acid from landing in one area of the pool. When too much acid is in one place, it can start deteriorating the surfaces in that area.

Can you add muriatic acid and chlorine at the same time?

No, these chemicals should always be added to the water separately. When chlorine and acids mix outside of the water, they create a toxic gas that can be fatal. Add muriatic acid to the water first, wait 30 minutes to 1 hour, and then add chlorine

Will muriatic acid clear up a cloudy pool?

It depends on the cause of the cloudy pool. If pH is too high, the acidity will be too low to dissolve the calcium in the water. The undissolved calcium will cause a pool to appear cloudy. Adding muriatic acid might also clear a pool with a pH value for the chlorine to be effective enough to kill algae in the pool.

Will muriatic acid lower hardness in a pool?

No, acids do not lower water hardness. Acids will dissolve calcium, but they will not remove it. Since muriatic acid does not remove calcium, the hardness level will not decrease it.

How long do you have to wait after putting muriatic acid in a pool?

The general recommendation is to wait 30 minutes to 1 hour for the muriatic acid to diffuse throughout the pool. After this waiting period, you can swim in the pool. You should also wait 30 minutes to 1 hour before adding chlorine to the pool.

Can I add a whole gallon of muriatic acid in my pool?

Some people add muriatic acid directly, but it is not a good idea. Muriatic acid is extremely caustic, even the fumes are dangerous, and it will likely permanently damage any surfaces that make direct contact. Using a 5-gallon bucket, you should dilute muriatic acid with pool water at a ratio of 10:1. To clarify, that means 1 cup of acid for 10 cups of water.

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