Home » How to Clean Pool Cartridge Filter (Using Muriatic Acid)

How to Clean Pool Cartridge Filter (Using Muriatic Acid)

Having a clean pool relies heavily on clean filter cartridges. The problem is, cartridge filter cleaning methods, like hosing, don’t deep clean a filter. But not to worry, this post reveals how you can easily clean your pool’s cartridge filter with muriatic acid.

Let’s dive in. 

Pool cartridge filter
Pool cartridge filter

How To Clean Pool Cartridge Filter(S) Using Muriatic Acid 

Cleaning your pool’s cartridge filter with muriatic acid is done as follows:

  1. Turn Off The Pool’s Pump
  2. Open The Filter Tank (Releasing the Pressure First) and Take Out The Cartridge Filter(s)
  3. Fill Up a Trash Can with a 20:1 Ratio of Muriatic Acid and Water 
  4. Soak the Cartridges in the Muriatic Acid Solution for 1 Hour
  5. Rinse Cartridges with a Garden Hose and Reinstall 

Read on for a detailed set of instructions on using acid to clean your pool’s filter cartridges.

Swimming pool cartridge filter pump
Swimming pool cartridge filter pump

What Clogs Up Cartridge Filters?

The cartridge filter in your pool keeps the water clean and safe. As the water goes through the cartridge filter, the elements in the filter trap floating debris in the water.

Over time, the filter picks up oils, dirt and calcium builds up on the filter elements which can clog the filter. This can be  tough to clear out by hosing or regular filter cleaner. When this happens, you should soak and wash the cartridge filter in muriatic acid.

Another thing that blocks up cartridge filters is DE (diatomaceous earth). Some pool owners have experimented by adding this to their filter. Read more in our article: Can You Add DE to a Cartridge Filter? (Answered!)

What You Need to Acid Clean Your Pool Filter

But before you can wash the cartridge filter in muriatic acid, you need a few things:

Filter Cleaning Instructions (detailed version)

Now let’s get to work. Here’s the detailed instructions for cleaning your pool’s filter with muriatic acid.

1. Turn Off The Pool’s Pump

The first step is a precautionary tip. You should never work on your pool’s equipment when the pump is turned on to prevent damages and personal injuries.

So, unplug or turn off the pool’s pump at the breaker.

2. Open The Filter Tank And Take Out The Cartridge Filter

The next step is to open the filter tank so you can have access to the cartridge filter.

Before you do, you must open (or bleed) the air relief valve to release the air pressure inside the filter tank. There is usually a lot of pressure in the filter tank. If you open the tank directly without releasing the air, the lid can pop off and cause injuries. So make sure to release the pressure first.

The filter tank is usually covered by a lid and this lid is clamped down using either an O-ring or a metal clamp that is held down with screws.

If your pool has an O-ring clamp, you should follow the directions in the owner’s manual to open it. Most O-ring clamps can be opened by pressing the release tab and turning the locking knob to the left (or in a counterclockwise direction).

If the filter tank lid is held down by a metal clamp and screws, you need to loosen the screws to allow you to open the filter tank. This is where the wrench will come in handy. 

When you open the filter tank, carefully pull out the cartridge filter.  Depending on the model of your pool, you may have more than one cartridge filter in the filter housing. So ensure to remove all the filters. 

3. Prepare the Filter Acid Cleaning Wash

You should never wash your cartridge filters with muriatic acid directly from the container. This is because the content of the acid will be too harsh on the elements and can damage the cartridge filter.

The acid is also strong enough to cause health issues. Make sure you use safety goggles, wear long sleeved clothing and acid resistant gloves.

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Mix the muriatic acid with water in a trash can to dilute the acid. A safe formula for cleaning pool filters is to mix the muriatic acid and water in the ratio of 1:20 parts. This means you should mix 1 part of acid in 20 parts of water.  

After mixing the acid with water, leave the solution for a few minutes to allow it to settle. 

Note: do not use cyanuric acid to clean your pool filter. Cyanuric acid and muriatic acid are very different. We have another article explaining the difference between cyanuric acid and muriatic acid.

4. Soak The Cartridge Filters in the Muriatic Acid Solution for 1 Hr

Carefully lower the cartridge filter into the muriatic acid solution and let it sit for one hour.

When you soak the filter in the muriatic acid solution, you may notice bubbles starting to form at the top of the solution – like air is escaping under the solution. This bubbling action shows that the filters are being cleaned. 

If you don’t notice any bubble formation, you don’t need to panic. Lack of bubbles means that the filter is not filthy. So top marks to you for great filter maintenance. 

After an hour, remove the cartridge filters from the solution.

If you still notice grime in the filter elements, you can use a very soft brush to stroke the pleats. This will get rid of any grime stuck in there. Never use a hard brush on the filter elements to prevent damages.

Note though that the filter will likely still look dirty after soaking – it will clear up nicely when we rinse it in the next step.

5. Rinse And Reinstall The Cartridge Filter(s)

After an hour, you should take the filter out of the acid solution and rinse it with your garden hose. Make sure to give the cartridge filter a hard spray with the garden hose. Doing that will ensure the filter is squeaky clean like you wanted.

Next inspect the cartridge filter for any damages. If the cartridge filter is worn out or damaged, that means it’s time for a replacement.

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Now reinstall it taking care to put the filter(s) back the same way they came out. 

How to Dispose Of The Muriatic Acid Solution

The acid solution you used to wash your filter is corrosive and you should neutralize it before disposing of it. You can neutralize it by using borax, baking soda and or soda ash. Simple add either one of these to the acid solution stirring as you go. 

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It will fizz, so make sure you have still got your safety equipment on. Keep adding either one of these until it stops fizzing.

You can now dispose of it down the sewer if your state or local laws allow it.

For detailed instructions, see our other post here.

Is it Safe to Clean the Pool Filter with Muriatic Acid?

Cleaning a pool’s filter with acid is safe to do. It should only be undertaken twice a year. Acid is strong and will break down the glues and materials in the filter so you want to limit how often you do this. You should always use a diluted acid solution and never 100% acid.

Now you know how to safely wash your cartridge filters using muriatic acid, but how often should you clean your pool filters? Let’s take a closer look.

Related Reading: Using Muriatic Acid To Clear A Green Pool Quickly

How Often Should You Wash Your Pool’s Cartridge Filter(S)?

You should wash your pool’s cartridge filter every month with a hose to ensure the top performance and durability of the filter elements. The filter(s) should be given a hard spray using your garden hose.

For a more thorough clean, use a cartridge filter cleaner. And for a deep clean, use muriatic acid – but only once or twice a year as it will degrade your filter.

Your pool’s cartridge filter traps a lot of dirt in the water. Algae, leaves, hair care products, body oils, and food residue are among the few contaminants that your filter elements trap in the water. Over time, these contaminants will accumulate in the filter elements and you will need to clear them. 

It is important not to let the debris in the filter elements accumulate, so you should rinse the filters with clean water every month or more in peak swimming season. You should also soak the cartridge filters in chemicals every 3 months.

You’ll need to clean your filter more if you use the pool a lot, have heavy rain or you’ve had algae in the pool. And if you have a lot of trees near your pool, cleaning your filter once a month will likely not be enough – try every week.

A good filter cleaning routine will ensure that your pool remains safe, clean, and healthy. But how do you know when the cartridge filters need cleaning? Keep reading to find out.

How Do You Know When To Clean Your Pool Cartridge Filter?

You can know when to clean your pool cartridge filter by checking the filter pressure gauge. The ideal filter pressure for a pool is between 8 PSI and 15 PSI (pounds per square inch). Any reading above this range is an indicator that you need to wash the cartridge filter.

Cartridge filter pressure gauge
Cartridge filter pressure gauge – You should look to clean your filter when the gauge is above 8-15 PSI (or whatever is normal for your system).

You should also clean it after heavy rain, lots of people swimming or after an algae outbreak.

Can You Backwash A Pool Cartridge Filter?

You should not backwash pool cartridge filters because it can damage the filter elements. Also, backwashing the filter elements doesn’t clean the filter particularly well. This is because part of the debris is deeply embedded in the filter elements and can’t be removed by hosing alone.

Instead, you can deep-clean the pool filters by soaking them in a pool filter cleaner. You can get a pool filter cleaner at any hardware store or pool store. Deep cleaning the filter will remove tough embedded stains like slime, algae, calcium build-up, oils and sunscreen. 

What Else Can I Soak My Pool Filter In To Clean It?

You can soak your pool filter in:

Spa Depot Pool Filter Cleaner

Spa Depot Pool Filter Cleaner

  • Cleans pleated spa/pool filter cartridges
  • Professional strength with enzymes
  • Won't cause water foaming
Check Price
Muriatic Replacement Acid

Muriatic Replacement Acid

  • Same powerful cleaning properties as muriatic acid, but with added benefits
  • Reduces the risk of corrosive damage to surfaces
  • Effective alternative to traditional muriatic acid
Check Price
Disclosure: We're industry experts and only recommend products we would use ourselves. This post contains affiliate links, so we may earn a small commission if you purchase through links on our site. There's no additional cost to you.

Many of the pool filter cleaners will contain acids. However, they will not be as strong as soaking in muriatic acid.


Overall, cleaning your pool’s cartridge filters with muriatic acid is a fairly easy process. All you need to do is mix the muriatic acid with water in the correct ratio and soak the cartridge filters in the solution. So give it a go and you’ll be surprised to see how well it works. 

Related Reading:
What Is Muriatic Acid for in a Pool?
Easy Way to Clean Algae from a Pool Filter Cartridge
Neutralize And Clean Up A Muriatic Acid Spill (Around A Pool)
What is a Normal Pool Filter Pressure Range?
Can You Convert Pool from Cartridge to A Sand Filter?