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How to Get Rid of White Water Mold and Pink Slime in a Pool

by Matt Giovanisci | Last Updated: March 27, 2020

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Does it look like your pool has a nasty cold? Do you see something that looks like mucus floating in the water, and covering pool surfaces? Yup, you’ve got a white water mold problem.

Or maybe you’ve noticed orangeish-pink streaks or spots around your pool’s water line, in the corners, on light fixtures and pipe fittings, or even on the water’s surface. You’re dealing with pink slime.

Fortunately, addressing both of these problems is as easy as preventing them from happening again in the future. All it takes is an understanding of what these substances truly are.

What Are White Water Mold and Pink Slime?

They’re two disgusting contaminants that may invade your pool from time to time. White water mold, like any mold, is a fungus. Pink slime, though sometimes mistaken for algae, is actually bacteria. The best treatment is prevention. Keep your pool clean and sanitized, and the water balanced.

What is White Water Mold?

Just like any other type of mold, white water mold is a type of fungus. All molds are fungi, but not all fungi are molds. For example, yeast is also a fungus, but it’s not mold, which is a good thing because without it, we wouldn’t have bread and beer. Then again, without mold, we wouldn’t have penicillin. Regardless, white water mold is not something you want in your pool.

What is That Pink Slime in a Pool?

Because of its appearance, you may have heard pink slime in a pool referred to as pink algae. But it’s not algae at all. It’s Serratia marcescens, also known as pink bacteria.

You’ve probably seen it before, in your home, most likely in your bathroom. Maybe along the bottom of your shower curtain, or around the water line in a toilet bowl. You may have heard some people say, “Oh, that’s just rust. We have hard water.”

It’s not rust. It’s an airborne bacteria that loves moist environments, especially bathrooms, because it feeds on the mineral deposits found in soap scum. It also likes fatty deposits found in soap and shampoo residue. Apparently, pink bacteria is not a picky eater.

Aside from being unsightly, it’s also dangerous. If the bacteria enters the body, usually through the eyes or nose, or via an open wound, it can cause numerous illnesses such as pneumonia, urinary tract infections, lower respiratory tract infections, to name just a few. For this reason, it’s all the more important to get rid of it when you find it in your pool, or better yet, keep it from occurring at all.

Important: Another place you may see pink bacteria in your home is in a pet’s water dish. If this happens, you must clean and sanitize the dish, and keep it clean to prevent illness. Serratia marcescens can cause or complicate urinary tract infections in dogs, and bacteremia in both dogs and cats.

What Causes White Water Mold and Pink Slime?

Just like any other type of fungus or bacteria, white water mold and pink slime are organic, naturally occurring substances.

If you find either one—or heaven forbid, both—in your pool, it’s due to two factors: your pool isn’t clean, and the water isn’t properly balanced.

Does Biguanide Cause White Water Mold?

No. This rumor persists for some reason, but no. Biguanide (which you may know under the brand name Baquacil) doesn’t cause white mold to grow in your pool.

In fact, biguanide can help get rid of it, if that’s the system you’re already using in your pool.

Whichever problem you have, the first step in getting rid of either mold or slime is going to be to clean your pool.

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May 26, 2020 2:48 pm UTC

How to Get Rid of White Water Mold in a Chlorine Pool

It’s important to be thorough in this process because even the smallest bit of white water mold left behind can multiply and go right back to being a big problem in no time.

1. Clean the Filter

If there’s white water mold in your pool, it’s probably in your filter too. So before you do anything else, clean the filter because you’ll need to use the filter later on to complete this process. It won’t be as effective if it’s infested with mold.

For this step, simply backwashing a sand or D.E. filter, or spraying the cartridge with a hose is enough, though you can also use filter cleaner if you want to.

2. Balance the Water

The most important level to balance is the pH. Make sure it’s between 7.4 and 7.6, with 7.5 being ideal.

3. Shock the Pool

A regular dose won’t be enough to kill the white water mold. You’ll need to triple or even quadruple shock your pool with chlorine shock. That means adding 3 or 4 pounds of calcium hypochlorite shock per 10,000 gallons of water.

If you’re not sure of your pool’s volume, you can use a pool calculator to figure it out before shocking.

Pool Volume Calculator Choose the shape of your pool first.
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Important: Remember, you need to shock your pool at dusk or night, so plan this process accordingly.

Calcium Hypochlorite Shock Calcium Hypochlorite Shock
$65.99
Use entire contents of bag when opened. If any granules settle to the bottom of the pool use brush to disperse. Add the recommended dosage of this product during evening hours while the filter pump is running.
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May 26, 2020 3:48 pm UTC

4. Brush the Pool

Using a stiff pool brush, thoroughly brush the pool’s bottom and walls. The goal is to brush as much of the white water mold off the surface as possible.

Check in and around the skimmer and return jets, behind ladders, and in shady spots of your pool where mold likes to lurk.

Heavy-Duty Aluminum Extra-Wide Pool Brush Heavy-Duty Aluminum Extra-Wide Pool Brush
$25.99

Strong and sturdy that will last for years. 20-inch extra-wide brushing that will cover large areas and finish cleaning quickly. Clean the most stubborn algae buildup quickly. The curved edges will help clean the hard corners very easy.

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May 26, 2020 6:47 pm UTC

5. Run the Pump

Overnight is good, but for 24 hours is even better. The idea is to get all the mold you brushed from the pool into the filter, so give it as much time as you can.

6. Brush the Pool Again

Think you got all the mold the first time around? Think again. You probably missed some, and if you leave it, everything you’re doing now will be for nothing because it’ll come right back.

So brush the sides and bottom of the pool again, and then let everything you brush up settle on the bottom.

7. Vacuum the Pool

An automatic pool cleaner won’t be enough for this job. You’ll need to manually vacuum the pool. Be sure to vacuum to waste.

Tip: Depending on how much mold and other debris you have to vacuum out of the pool, the water line may drop too low. Have a garden hose handy to refill as necessary.

8. Clean the Filter Again

This time, definitely use a filter cleaner for a sand or D.E. filter, or a chemical soak for a cartridge filter.

9. Test and Balance the Water

You can use test strips or a liquid test kit, or take a sample of pool water to your local pool store and have them test it for you. Make sure you bring the pH, alkalinity, and especially the chlorine back up to the right levels.

Note: Yes, you do need to repeat a couple of steps. That should be an indication of what a problem white water mold is, and how difficult it can be to get rid of it. Be patient and thorough, because repeating a couple of steps is better than repeating the entire process if any mold is left behind.

Digital Water Test Kit for Pools and Hot Tubs Digital Water Test Kit for Pools and Hot Tubs
$169.95
This digital pool and hot tub water test kit checks for Free Chlorine, Total Chlorine, Bromine, PH, Alkalinity, Calcium Hardness, and Cyanuric Acid.
If you click this link and make a purchase, we earn a commission at no additional cost to you.
May 26, 2020 6:47 pm UTC

Keep an Eye Out for More Mold

You’ll want to closely monitor your pool for a few days to a week after this cleaning process to make sure the white water mold doesn’t return.

During that time, run the pump as often and for as long as you can. Also, brush and vacuum the pool every other day, just to be sure.

How to Get Rid of White Water Mold in a Biguanide Pool

This process will be very similar to the one for a chlorine pool, just with different chemicals and a couple of slight adjustments.

1. Clean the Filter

If there’s white water mold in your pool, it’s probably in your filter too. So before you do anything else, clean the pool filter because you’ll need to use the filter later on to complete this process. It won’t be as effective if it’s infested with mold.

For this step, simply backwashing a sand or D.E. filter, or spraying the cartridge with a hose is enough, though you can also use filter cleaner if you want to.

2. Balance the Water

The most important level to balance is the pH. Make sure it’s between 7.4 and 7.6, with 7.5 being ideal.

3. Use an Oxidizer

Remember, biguanide sanitizer doesn’t oxidize contaminants, so you must supplement it with an oxidizer. Also, you can’t use regular shock—chlorine or non-chlorine—in a biguanide pool.

A regular dose won’t be enough to kill the white water mold. You’ll need to use a triple or even quadruple dose. That means adding 3 or 4 gallons of oxidizer per 10,000 gallons of water.

If you click this link and make a purchase, we earn a commission at no additional cost to you.
May 26, 2020 6:47 pm UTC

4. Brush the Pool

Using a stiff pool brush, thoroughly brush the pool’s bottom and walls. The goal is to brush as much of the white water mold off the surface as possible.

Check in and around the skimmer and return jets, behind ladders, and in shady spots of your pool where mold likes to lurk.

5. Run the Pump

Overnight is good, but for 24 hours is even better. The idea is to get all the mold you brushed from the pool into the filter, so give it as much time as you can.

6. Brush the Pool Again

Think you got all the mold the first time around? Think again. You probably missed some, and if you leave it, everything you’re doing now will be for nothing because it’ll come right back.

So brush the sides and bottom of the pool again, and then let everything you brush up settle on the bottom.

7. Vacuum the Pool

An automatic pool cleaner won’t be enough for this job. You’ll need to manually vacuum the pool. Be sure to vacuum to waste.

Tip: Depending on how much mold and other debris you have to vacuum out of the pool, the water line may drop too low. Have a garden hose handy to refill as necessary.

8. Clean the Filter Again

This time, definitely use a filter cleaner for a sand or D.E. filter, or a chemical soak for a cartridge filter.

If you click this link and make a purchase, we earn a commission at no additional cost to you.
May 26, 2020 6:47 pm UTC

9. Test and Balance the Water

You can use test strips or a liquid test kit, or take a sample of pool water to your local pool store and have them test it for you. Make sure you bring the pH, alkalinity, and especially the chlorine back up to the right levels.

10. Add Algaecide

Important: You won’t do this step until 5 to 7 days after completing the cleaning process.

We don’t normally recommend using algaecide. But a biguanide algaecide does more than fight algae. It also works with the sanitizer and oxidizer to kill and prevent white water mold.

Add 4 ounces of biguanide algaecide for every 10,000 gallons of water in your pool. You can continue to do this once a week for regular maintenance, if you like.

If you click this link and make a purchase, we earn a commission at no additional cost to you.
May 26, 2020 6:47 pm UTC

Note: Yes, you do need to repeat a couple of steps. That should be an indication of what a problem white water mold is, and how difficult it can be to get rid of it. Be patient and thorough, because repeating a couple of steps is better than repeating the entire process if any mold is left behind.

Keep an Eye Out for More Mold

You’ll want to closely monitor your pool for a few days to a week after this cleaning process to make sure the white water mold doesn’t return.

During that time, run the pump as often and for as long as you can. Also, brush and vacuum the pool every other day, just to be sure.

Frustrated by adding chemicals and trying to keep your pool clear all the time?

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Click here to learn more
The Pool Care Handbook

How to Get Rid of Pink Slime in a Chlorine Pool

Unfortunately, pink bacteria is resistant to most of the chemicals you use to clean and sanitize your pool, even chlorine. So the usual cleaning processes and sanitizer doses just won’t do.

1. Clean the Filter

If there’s pink bacteria in your pool, it’s probably in your filter too. So before you do anything else, clean the pool filter because you’ll need to use the filter later on to complete this process.

For this step, simply backwashing a sand or D.E. filter, or spraying the cartridge with a hose is enough, though you can also use filter cleaner if you want to.

If you click this link and make a purchase, we earn a commission at no additional cost to you.
May 26, 2020 6:47 pm UTC

2. Balance the Water

The most important level to balance is the pH. Make sure it’s between 7.4 and 7.6, with 7.5 being ideal.

3. Turn off the Pump

You’ll be adding some chemicals to the water, and you don’t want them to circulate just yet.

4. Brush the Pool

Using a stiff pool brush, thoroughly brush the pool’s bottom and walls. The goal is to brush as much of the pink bacteria off the surface as possible.

Check in and around the skimmer and return jets, behind ladders, and in shady spots of your pool where bacteria likes to lurk.

5. Add Algaecide (Sort Of)

We’ve already established that pink slime is bacteria and not algae. Yet, because so many people refer to it as pink algae, some companies have created products to address the problem as it’s popularly known.

So look for an “algaecide” that specifies it’s for treating pink slim or pink bacteria. One such brand is Pink Treat.

United Chemicals Pink Pool Treat Algaecide United Chemicals Pink Pool Treat Algaecide
$39.36
Helps control blooms of red and pink algae. Plus controls white slime, pink, and white water mold in pools treated with chlorine or bromine.
If you click this link and make a purchase, we earn a commission at no additional cost to you.
May 26, 2020 3:48 pm UTC

Follow the manufacturer’s instructions on the package to add the appropriate amount for your pool’s volume.

6. Shock the Pool

A regular dose won’t be enough to kill the chemical-resistant pink bacteria. You’ll need to triple or even quadruple shock your pool with chlorine shock. That means adding 3 or 4 pounds of calcium hypochlorite shock per 10,000 gallons of water.

Test the water between each application of shock. The goal is to bring the chlorine level up to 5 parts per million (ppm).

Important: Remember, you need to shock your pool at dusk or night, so plan this process accordingly.

7. Take a Break

With the pump still off, let the pool sit overnight.

8. Vacuum the Pool

An automatic pool cleaner won’t be enough for this job. You’ll need to manually vacuum the pool. Be sure to vacuum to waste.

Tip: Don’t allow the water line to drop too low. Have a garden hose handy to refill as necessary.

9. Clean the Filter Again

This time, definitely use a filter cleaner for a sand or D.E. filter, or a chemical soak for a cartridge filter.

10. Run the Pump

Keep it on as you normally would.

11. Keep the Chlorine Level High

For about a week after this treatment, keep the chlorine level at 5 ppm. You’ll need to test the water every day to ensure you’re maintaining this level.

The easiest way to test that often is with test strips or a liquid test kit.

AquaChek Select 7-in-1 Pool and Spa Test Strips AquaChek Select 7-in-1 Pool and Spa Test Strips
$15.89
Tests for 7 important chemistries in seconds: Total Hardness, Total Chlorine, Total Bromine, Free Chlorine, pH, Total Alkalinity, and Cyanuric Acid.
If you click this link and make a purchase, we earn a commission at no additional cost to you.
May 26, 2020 6:47 pm UTC

12. Balance the Water

After a week, allow the chlorine level to drop back to normal, then balance the water as you normally do, bringing all levels to where they should be.

How to Get Rid of Pink Slime in a Biguanide Pool

This process will be very similar to the one for a chlorine pool, just with different chemicals and a couple of slight adjustments.

1. Clean the Filter

If there’s pink bacteria in your pool, it’s probably in your filter too. So before you do anything else, clean the pool filter because you’ll need to use the filter later on to complete this process.

For this step, simply backwashing a sand or D.E. filter, or spraying the cartridge with a hose is enough, though you can also use filter cleaner if you want to.

2. Balance the Water

The most important level to balance is the pH. Make sure it’s between 7.4 and 7.6, with 7.5 being ideal.

3. Turn off the Pump

You’ll be adding some chemicals to the water, and you don’t want them to circulate just yet.

4. Brush the Pool

Using a stiff pool brush, thoroughly brush the pool’s bottom and walls. The goal is to brush as much of the pink bacteria off the surface as possible.

Check in and around the skimmer and return jets, behind ladders, and in shady spots of your pool where bacteria likes to lurk.

Add Biguanide Algaecide

Remember, you cannot use regular algaecide—or the pink-specific “algaecide”—in a biguanide pool. Add 16 ounces of biguanide algaecide for every 10,000 gallons of pool water.

3. Add an Oxidizer

Remember, biguanide sanitizer doesn’t oxidize contaminants, so you must supplement it with an oxidizer. Also, you can’t use regular shock—chlorine or non-chlorine—in a biguanide pool.

A regular dose won’t be enough to kill the chemical-resistant pink bacteria. You’ll need to use a triple or even quadruple dose. That means adding 3 or 4 gallons of oxidizer per 10,000 gallons of water.

4. Raise the Sanitizer Level

The usual range for biguanide is 30 ppm to 50 ppm. To kill the pink bacteria, bring the biguanide level up to 50 ppm.

6. Take a Break

With the pump still off, let the pool sit overnight.

7. Vacuum the Pool

An automatic pool cleaner won’t be enough for this job. You’ll need to manually vacuum the pool. Be sure to vacuum to waste.

Tip: Don’t allow the water line to drop too low. Have a garden hose handy to refill as necessary.

Recheck the Sanitizer Level

Make sure the biguanide level is still at 50 ppm. If it’s fallen, add more biguanide to bring it back up.

8. Clean the Filter Again

This time, definitely use a filter cleaner for a sand or D.E. filter, or a chemical soak for a cartridge filter.

9. Run the Pump

Keep it running continuously until the water clears.

11. Balance the Water

Once the water clears, allow the biguanide level to drop back to within the normal range, then balance the water as you normally do, bringing all levels to where they should be.

Keep an Eye Out for More Bacteria

You’ll want to closely monitor your pool for a few days to a week after this cleaning process to make sure the pink bacteria doesn’t return.

During that time, run the pump as often and for as long as you can. Also, brush and vacuum the pool every other day, just to be sure.

How to Prevent White Water Mold and Pink Slime in Your Pool

Whew! After all that work, you’ll want to make sure you keep that mold and bacteria where it belongs—out of your pool!

The best ways to prevent either invasion are to keep your pool clean (and we mean clean), keep the water balanced (especially the pH and sanitizer levels), and shock regularly (or use an oxidizer for a biguanide pool).

No More Pink, White and Blue for You!

Just when you thought it was safe to go back into the water—it is! After putting in all that hard work, you deserve to enjoy your pool. Just stick to your pool care schedule to keep that white water mold away, and don’t allow the pink slime back in your pool. A little maintenance goes a long way to keeping your pool clean, clear, and swimmable.

Happy Swimming!

Matt Giovanisci, the founder of Swim University®, started in the pool and spa industry at age 13 and moved to bigger companies along the way, helping thousands of pool and hot tub owners every year. He wanted to share his knowledge and unique teaching style on a larger scale, so he launched Swim University® in 2007. Since then, he's worked to make pool and hot tub care easy for over 10 million homeowners. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.

Frustrated by adding chemicals and trying to keep your pool clear all the time?

We cut out all the confusion of pool maintenance in this easy-to-read illustrated ebook and video course. It'll help you save $100 right away on pool care!

Click here to learn more
The Pool Care Handbook

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