How To Acid Wash A Pool (With And Without Draining)



Got a grungy pool with a lot of unsightly stains from years of use?

Wanna know how you can restore your pool to its original glory?

Then you should learn how to acid wash a pool! It’s really not that difficult to do, but you do need to fully comply with all the safety precautions. 

Permit us to explain…

What Is Acid Washing?

While regular maintenance of your pool requires things like vacuuming, brushing the pool walls, and removing scale, acid washing is a bit more involved.

Acid washing is the process of restoring a pool’s finish using a chemical called muriatic acid. It entails coating the finish with a diluted solution of the acid, gently brushing the walls and floor, and rinsing everything off. 

Muriatic acid is highly toxic, and exposes your finish by stripping away the top layer of plaster, removing stains, dirt, and mold that may have accumulated over the years.

Pools with plaster, aggregate, or tile finishes can be acid washed. However, above ground pools, and pools with a vinyl liner should never be cleaned this way as the acid will eat right through them.

When Should You Acid Wash Your Pool?

You should wait at least 5 years between acid washes. This ensures you won’t damage the finish due to frequent exposure.

Here are some situations that may call for it:

  • Years of Use: Being exposed to harsh chemicals and constant sunlight can eventually dull and discolor a pool’s finish, which acid washing can restore.
  • Algae: Pool algae can be controlled and even eradicated in most cases with algaecide. But sometimes, leftover spores can produce new blooms. Acid washing will fully eliminate them.
  • Lots of Stains: A buildup of stains from chlorine, minerals, dirt and other debris can be easily cleaned with an acid wash.
  • Prolonged Stagnation: If you leave your pool sitting stagnate too long, staining can occur (especially on plaster finishes). You should also ensure you properly winterize your pool, so stains don’t build up over the winter months.
  • Repairing: If repairing an area of the finish, you should acid wash it first. This will eliminate things like existing algae or mold spores from mixing with the new finish and eventually getting into the pool.

How Do You Acid Wash A Pool?

If you’ve decided to acid wash your own pool, we cannot stress enough how important it is to do this safely. Muriatic acid is a highly corrosive chemical, so you want to take every precaution necessary when using it. 

Step 1. Pre-Wash Checklist

First things first – only acid wash when 2 conditions are met: 

1. The weather is on the cooler side

2. There is ZERO wind present

Cooler weather is ideal because plaster and aggregate finishes can dry out and crack if they’re left exposed and baking in the sun.

Doing an acid wash on a non-windy day is vitally important. You’ll be applying the acid using a sprayer, and you’ll need to avoid liquid or fumes blowing back at you, or anyone else that is helping with the wash.

Step 2. Prep The Pool

To fully clean the pool’s walls, you’ll need to start by draining the water from the pool. Once emptied, scoop up any remaining debris that may be left around the drain and toss it out.

Using a garden hose, spray down the walls to get rid of any light debris that may be left over. At this point, we also recommend clearing the pool deck of any obstructions, and locking up any kids or pets so they aren’t exposed to any chemicals. 

Step 3. Suit Up

Next up is to fully cover yourself from head to toe in protective gear.

This means long sleeves and pants, chemically-resistant rubber gloves, goggles, galoshes or waterproof work boots, and a respirator mask that is designed for working with chemicals – specifically acid fumes.

Remember, muriatic acid is highly toxic and can produce fumes that will send you to the ER. Do not acid wash unless you have the right mask for the job!

Additionally, you’ll need a pump sprayer with an applicator wand for easy and even distribution of the acidic solution, a chemically-resistant hard-bristled brush on a long pole, and a second person using a garden hose to rinse the pool walls.

Step 4. Dilute The Acid

IMPORTANT – Diluting muriatic acid can only be done by adding acid to water. Do not ever add water to acid, as it can boil over and splash outside of the container – which you don’t want! 

Be very careful handling the acid mixture because acid burns will leave permanent damage on your pool finish or deck if it spills.

The dilution ratio you want to use is 1:10 – that’s 1 part acid into 10 parts of water.

For example, if you’re using a 2.5 gallon pump sprayer (equivalent to 10 quarts), the one-tenth ratio of acid required would be 1 quart, or 4 cups.

Step 5. Spray ‘N Scrub

Now comes the fun part. 

Starting in the deep end of the pool, pump up the sprayer and then apply the solution using the applicator wand. 

You’ll want to apply relatively quickly, from left to right, in about 5 foot lengths, moving from the top to the bottom of the pool wall.

Once this 5-foot section is covered, use the bristled brush to move the solution around and gently scrub it into the finish. The acid will do most of the work so don’t feel like you need to use a lot of elbow grease here.

Again, you want to work quickly but safely. Don’t rush the job, just be efficient.

Step 6. Rinse & Repeat

After 60 to 90 seconds, the acid is ready to be rinsed off. This is where having a second person comes in handy. They can sit ready with a timer and garden hose, rinsing the walls when the time is right.

This frees you up to focus on repeating step 5 around the deep end walls, working your way to the shallow end of the pool.

When cleaning horizontal surfaces (ie. steps, swim-outs), ensure they’re repeatedly rinsed, as any remnants of acid will eat away at them.

Step 7. Neutralize The Wastewater

With fully-cleaned walls, you’re gonna end up with a lot of wastewater around the pool’s drain. 

While the acid becomes a further diluted solution due to the rinsing, there is still enough of it to be potentially harmful. For this reason, you need to neutralize it before pumping it out.

You can do this by adding 2 lbs. of soda ash per 1 gallon of solution used and stir it up using your brush. 

Step 8. Pump Out The Water

Even with the wastewater neutralized it can still potentially harm plant life and animals, so be careful where you decide to pump it out to. 

Using a submersible pump, run the hose out of the pool either up the deep end wall, or out the shallow end for a less steep incline. Pump the water out.

Rinse the entire pool, pump again, and for good measure, repeat the process a third time and you’re done!

Can You Acid Wash A Pool Without Draining?

If you want a safer method of how to acid wash a pool, you can do a no-drain acid wash just by letting your pool water’s pH level drop.

A balanced pH level for pool water is 7.4, but a 1.0 pH level is highly acidic. While it isn’t as effective as a muriatic acid wash, it can still help in removing stains and dirt from pool walls.

How To Do A No-Drain Acid Wash

The no-drain acid wash is a 3-day process (ideally in cool, agreeable weather), where you drop the pool water’s pH and alkalinity to low, acidic levels. This creates a corrosive environment for the water to eat away at things like scale and stains. 

Here’s a quick how-to guide for a no-drain acid wash:

  1. First you need to prep the pool. The week before the wash, over-filter and over-sanitize the pool. Make sure it’s thoroughly cleaned with a brush and a vacuum. You want it as sparkling as you get it.
  1. Next, you’ll need to remove any metals from the pool as highly acidic water will destroy them if they’re left in during the wash. Get rid of ladders and pool lights, as well as cleaners and accessories. The pool needs to be empty.
  1. Top the pool up with water to the top of the trim, or slightly drain it to the bottom of the trim. After this is done, shut off your pump and pool filter.
  1. Now you have to begin to drop the pool’s pH level. This can be done by using a metal sequestrant (16 ounces per 10,000 gallons) and pH Decreaser (8 lbs. per 5,000 gallons).
  1. Test the water to make sure Total Alkalinity is dropped to zero. If not, add more pH Decreaser until you hit that target.
  1. For the next 72 hours, clean the pool with a steel pool brush daily, and retest the water daily to make sure it’s staying in the proper acidic range.
  1. When the 3 days are up, begin to reverse the water, raising the pH level and alkalinity. You can do this with a pH Increaser (8 lbs. per 5,000 gallons).

Proceed With Caution

For any pool owner, learning how to acid wash their pool can come in handy down the road.

While you can hire professionals for this service, they often charge a lot due to the labor and use of highly hazardous chemicals.

As long as you have some DIY spirit, you’ll be fine. But always, always, always, practice proper safety procedures if you go this route. Don’t say we didn’t warn you!

Categories: Pool Care, Pool Maintenance