How to acid was a pool

Every five years or so, after enough time has passed to allow deep stains to seep into your pool’s walls and bottom, it’s time to give your pool a much more thorough cleaning than usual.

We’re not just talking about steel brushes and a firm hand – we’re talking about getting real chemical assistance. In this case, acid is an unbelievably potent tool for giving your pool a thorough cleaning – provided it’s used efficiently, responsibly, and quickly.

However, using acid to clean out your pool is also a very involved process, and one that can be quite dangerous without the proper precautions (and still carries some risk with proper precautions). Read on to learn more about how to acid wash your own pool – but know that you’ve always got the option of hiring a pro.

What is an acid wash?

An acid wash is a thorough deep cleaning of a cement or concrete pool’s walls and flooring with a diluted acid mixture. Before a pool can be acid washed, it needs to be completely drained – which is why this is not only a serious time sink but a big financial investment as well.

Although you should dilute the acid thoroughly, you are still going to be working with a highly caustic substance and need to scrub and neutralize quickly and efficiently to avoid damaging your pool. Because an acid wash is a very potent cleaning method, it usually only needs repeating once every few years (with the exception of severe staining, such as after a major algae bloom).

When should you acid wash your pool?

There are a few signs that point towards a future acid wash: severe stains, heavy algae blooms (which can leave behind spores in your walls), long-term stagnation (such as ignoring a pool for years, or not winterizing), as well as general wear and tear over the years.

Here’s what you need for an acid wash

The prep sheet for a thorough acid wash is understandably long. We’re looking at completely draining a pool, soaking its walls in an acid mixture, and giving it a thorough scrub while standing inside the dry pool. A couple of things you’ll need on hand include:

  • An acid of your choice (muriatic pool acid is the most common).
  • A chemical-resistant pail/bucket (at least five gallons).
  • Several pool brushes (soft as well as hard bristles).
  • A liquid vacuum or submersible pump.
  • Lots of soda ash (strong base to neutralize the acid after cleaning).
  • A high-quality acid fume mask.
  • High-quality chemical-resistant work boots and gloves.
  • Safety goggles.
  • Thick, long-sleeved clothing.
  • Long garden hoses.

Do NOT skip out on anything on this list. Muriatic acid, or any strong acid for that matter, is exceptionally dangerous – even a drop can scar you, and the fumes can be enough to cause damage to your airways, eyes, and mucus membranes.

Other necessary precautions

Aside from having all the right equipment to handle pool acid, be sure to imprint a few key golden rules into your acid wash job:

  • Always add acid to water. Never the other way around. Adding water to acid can cause a boil-over due to the near-instant thermal reaction, which can cause the acid to splash onto the floor, and onto your clothes, etc.
  • Make sure you’re blocking the area off from kids and pets. If you have a partner, consider letting them take the kids and pets away for the day while you acid wash the pool.
  • Always handle your acid VERY SLOWLY. Sudden movements can cause spillage or splashes, which will hurt.
  • If you get any acid on you, rinse with water immediately, for several minutes, and call emergency services.
  • Always keep your acid containers tightly sealed when you aren’t in the process of using them, even if you’re only setting the container down for a few seconds.
  • Never hold your face near the top of an acid container, even if just to check how much you’ve got left.

Now, let’s go over the steps together:

First, drain your pool

Pool draining is a topic in and of itself. In general, you should contact a professional to drain your pool, especially if it’s an inground pool, and especially if you’ve never done it before. As always, check with your municipality to figure out when and how you can dispose of your pool water, as well as the wastewater you’ll be disposing of throughout the acid washing process.

After your pool has been completely drained, be sure to replace and replug your valves. You don’t want your acid mixture (despite being diluted) to seep heavily into the ground water.

Prepare your acid wash

Start with a 1:1 ratio of acid to water. You can use less acid to begin with – not only might it be enough to do the trick if you have minor stains, but it will also save you a lot of money in the process.

Fill a bucket halfway with water, and slowly (very slowly) pour your acid. You’ll want to do this several times throughout the process, so be sure to keep the acid nearby (and tightly sealed).

Prepare your acid wash

Start with a 1:1 ratio of acid to water. You can use less acid to begin with – not only might it be enough to do the trick if you have minor stains, but it will also save you a lot of money in the process.

Fill a bucket halfway with water, and slowly (very slowly) pour your acid. You’ll want to do this several times throughout the process, so be sure to keep the acid nearby (and tightly sealed).

Hose the pool

Before you pour any of your diluted acid onto the pool wall, be sure to wet that spot thoroughly with a hose. You might want multiple hoses for this. Keep them running.

Pour, scrub, wash, repeat

You’ll have to wash your pool procedurally, one portion at a time. Distribute the bucket over a large portion of the pool, then use a long-handled pool brush to scrub away at the stains. Let the mixture set for at least 20 minutes before hosing it down completely. Never pour your acid on dry plaster. Always make sure the area you’re pouring your acid onto is wet first.

Neutralize the acid

Once you’ve given the pool a once-over, use your soda ash to neutralize the acid wastewater that’s gathered at the bottom. If you’ve kept the water running, it should have been continuously diluted. You can use a water test strip on the wastewater to check its pH. Bring it up to about 7.0 pH before pumping the wastewater out of the pool.

Remove the wastewater

Your disposal methods for the acid wash wastewater will depend on your local municipality’s environmental rules. You may be allowed to pour it down the street or let it flow into your city’s canalization. Be sure to ask the local authorities via call or email, or let your homeowner’s association know.

Once you’ve pumped or drained out the neutralized wastewater, you might need to scrub the bottom of your pool again to remove any staining caused by the standing waste. Use a diluted acid mixture if the staining doesn’t go away with the brush and water. Neutralize and remove the ensuing wastewater again.

Fill your pool

We’ve gotten to the last step! Once you have properly disposed of the last round of wastewater, and are satisfied with the state of your pool, it’s time to start refilling it. Obviously, this can take a long time.
If you’re using an average half-inch garden hose and are filling your poll up at a rate of about 500 gal/h, for example, you should plan to keep it running for at least ten hours to fill up a 5,000-gallon pool – and double, triple, or even four times that for larger pools. Bigger hoses will shorten the filling time, provided your water pressure keeps up.


At the end of the day, thoroughly acid washing a pool is a big job – and one you should only have to commit to about once every five years or so, anyway. While it isn’t particularly difficult to acid wash a pool, it does take up the better part of your day – and involves carefully handling industrial amounts of acid.

If you’re uncomfortable handling a large amount of acid, properly neutralizing it multiple times, aren’t sure how to properly or carefully dispose of the wastewater in your municipality, or are worried about draining your pool by yourself, you can (and should) always hire a professional to get the job done. You’ll end up with less of a mess, much more time on your hands, and potentially fewer costs (and much fewer risks).

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