How to Treat and Quickly Remove Algae From Your Pool

Written by Michael Dean
October 12, 2023

treating pool algae

Just woke up to a green pool? Finding algae growing in your pool can be frustrating because no one wants to swim in filthy green water! Algae can become a huge problem in a very short amount of time, and many new pool owners don’t realize how fast it can grow. There are many ways to prevent algae from growing and effective treatment options if it has already started growing. But first, let’s cover how algae forms and the types of algae in swimming pools.

If you’ve already identified the algae in your pool, feel free to jump right to my steps to clean it up.

Main Takeaways

  • Poor sanitation and circulation are common causes of algae growth in pools.
  • Depending on how dark the green algae infestation is in your pool, you’ll have to add more shock to effectively kill it. For example, a light green infestation only needs double the pool shock, while black green algae requires four times the pool shock.
  • If left untreated, pool algae can harm swimmers and stain or damage your pool surfaces and equipment.

How Algae Forms in a Pool

Algae is always present in water, but you can only see it when it “blooms” since it is a microscopic organism. Blooming is the process in which algae grows, feeds, and multiplies. Algae can also transfer in larger quantities from people’s bodies or swimsuits contaminated by other water sources.

Most of the time, algae blooms because of inadequate sanitation due to poor filtration or improper chemical levels. It can also form because some areas of your swimming pool are not circulating enough. Prime real estate for algae growth includes under rails, in corners, and other sheltered locations where treated water may not circulate properly.

Algae will thrive in a pool that has gotten a lot of use. The algae blooms will feed on almost anything, including dead skin cells, oils, sweat, and garden fertilizer. There are a few different types of algae, and you need to treat each one slightly differently. Let’s dive into those types.

Types of Algae and How They Differ

There are over 21,000 types of algae that you can find in swimming pools. They are generally grouped into a few different categories. Green, black, and yellow algae are similar but have slight differences in treatment. There is also a pink slime that is often mistaken for algae, but it is actually a bacterial film. More on that one in a bit.

Green Algae

Green algae is the most common type of algae and the easiest to treat. It may form on the sides of the pool, or it may be free-floating (see the example below for what it looks like). Green pools occur when enough free-floating algae blooms are present in the water. A lack of proper sanitation often causes it, but a chlorine chemical shock can remove it. For green algae, I generally recommend using double the average quantity for the chemical shock. However, if your pool is a darker shade of green, you may need to use more shock than if it is a lighter shade. Here is a breakdown of how much shock to use depending on the shade of your green pool.

Light Green (Teal)

This is the easiest to clear up, and the newest green algae bloom. Use two times your standard shock amount to kill this algae infestation and monitor your chemical levels, and keep an eye out for new algae growth.

Dark Green

This is when the algae has significantly grown and taken over your pool; the shade will be a much darker green and will require three times the standard shock amount to treat.

Black Green

At this point, your pool looks like a swamp, and it is almost impossible to see the bottom of the pool. Your pool will smell very strongly of algae at this point (yuck!). Black green algae has had the longest time to multiply and is by far the most difficult to kill; you’ll need at least four times the standard shock treatment for black green algae.

Yellow Algae

Also called mustard algae or brown algae, this variety will appear on sheltered surfaces. Yellow algae will stick to the floors and sides of the pool and is more challenging to remove than green algae. To clear out yellow algae, brush the walls and floors aggressively, shock your pool with three times the amount of chlorine you would use for a typical shock treatment, and run the pump and filter for 24 hours.

Black Algae

Black algae usually shows up as dark spots on the walls, and it is highly persistent but relatively rare (image below with an example). Black algae has a hard outer shell that protects the cells inside, making removal very difficult, but not impossible. To remove black algae from your pool, vigorously scrape your swimming pool walls and shock your pool with four times the amount of chlorine you would use for a typical shock treatment.

Pink Slime

Often misconstrued as algae, pink slime is actually a bacteria that forms a slimy pink or transparent layer over the pool’s surface. Regular brushing and vacuuming can decrease the chance of pink slime. If your pool does start forming pink slime, shock your pool and leave the filter on for 24 hours.

How to Get Rid of Algae In Your Pool Fast

The two primary chemical treatments for algae are chlorine and flocculant.

How to Use Chlorine Shock to Remove Algae Fast

Chlorine shock is the most common method used for dealing with algae. You can usually dose twice the usual shock for green algae, three times for yellow algae, and four times for black algae. However, chlorine shock will not work correctly if the algae are attached tightly to the walls or floor. Because of this, you must use a brush to loosen the algae before shocking it.

Here are the steps you need to take to use chlorine to remove algae.

  1. Vacuum your pool. Make sure to use a manual pool vacuum to bypass your filter and go directly to the waste. The last thing you want is the algae recirculating in your system.
  2. Brush your pool walls. This brushing may be hard work, but it will ensure that the sanitizer does its job in killing all of the algae. Check out my guide on the best pool brushes for a recommendation.
  3. Test and balance your pool chemistry. Use a test kit to check for total alkalinity and pH levels. Doing this allows for the sanitizer to be at its most effective state.
  4. Wait until the right time. Chlorine reacts to sunlight, so it’s best to wait until the sun goes down before shocking your pool.
  5. Calculate your shock levels. Algae is tough, so you’ll want to at least double up on your shock levels. Multiply the shock amount by 2 for green algae, 3 for mustard algae, and 4 for black algae.
  6. Prep your shock. Prepare the shock ahead of time by dissolving the chlorine in a 5-gallon bucket of pool water and stirring. Skip this step if you’re using liquid shock. If you’re unsure what to use, head to my guide on the best pool shock.
  7. Shock your swimming pool. Ensure the pool pump is running and pour the mixture from the bucket into the water around the edges of the pool. For more details, read my article on how to shock your swimming pool.
  8. Let the filter run and test again. Let the pump and filter run for 6-8 hours to ensure all the dead algae is filtered out of the water. You will be able to visualize a change in the clarity of the water. After waiting, test the water again to ensure the chemical levels are safe before swimming. Make sure you check and adjust your pH, alkalinity, chlorine, cyanuric acid, and calcium hardness levels as needed.
In The Swim Calcium Hypochlorite Chlorine Granular Pool Shock

In The Swim has a reliable cal hypo shock that is effective and easy to use.

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If the algae still won’t go away after shocking, read my article on what to do if your pool is still green after shock and algaecide.

How to Use Flocculant to Quickly Remove Algae

Flocculant, or floc, is a chemical used to clear up algae or cloudy pool water. Flocculant works very quickly and clears cloudy pool water by clumping small particles together and dropping them to the bottom of the pool to be vacuumed out. To get rid of little green algae quickly, I recommend using floc with the following steps.

  1. Raise the water level in your pool. A necessary step as you will end up vacuuming a lot of water out.
  2. Dilute the flocculant. Follow the directions on the container of the floc you are using and dilute it with water in a bucket as instructed.
  3. Pour the diluted flocculant. Once the floc is diluted, pour it around your pool near the pool walls for maximum effectiveness. Allow the floc to circulate in the water for about two hours.
  4. Wait for the clumps to form. After shutting your pump off, the floc will bind to the algae and settle on the pool floor. Let the clumps sit overnight if possible.
  5. Turn the multiport valve to waste. The waste setting will ensure dirty water doesn’t filter back into your pool.
  6. Vacuum the pool. Remove all the sediment collected at the bottom of the pool.
  7. Add more water. After vacuuming, you will need to add replacement water.
  8. Run your filter. Let your filter run until the water clears up and all the dead algae is removed.
BioGuard Powerfloc

This solution from BioGuard is really effective and is what I use when I need a powerful flocculant.

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How to Get Rid of Algae with Non-Chemical Treatments

There are two major types of non-chemical solutions for algae: ultrasonic waves and UV light. These are primarily used to prevent algae from blooming rather than clearing up algae that already exists. Still, if you have a minor algae problem, you might be able to use one of these methods. To do this, you must first balance the chemicals in the water as usual, improve circulation, and brush the walls.

Sonic and UV cleaners attach to your filtration system, typically after the water has been run through the filter to clean it mechanically. These devices are highly effective at killing algae that comes through them. On the other hand, they will not affect algae they do not come into contact with. For this reason, I would recommend using them as a preventive measure instead of a treatment process.

Read my complete guide on how to clear green pool water to learn more!

Here’s a good video describing some of the algae removal processes I outlined above.

Get My Free Pool Care Checklist

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Tips to Prevent Swimming Pool Algae from Coming Back

The last thing that you want after finally getting your algae under control is prevention. Luckily, algae in pools is easier to prevent than get rid of. Invest a little time to work on preventing algae blooms to avoid a future headache.

The main preventative treatments for algae are:

Sanitation: Maintaining balanced water and chemical levels is crucial for any pool owner’s routine.

Circulation: Keeping the water moving will prevent the likelihood of algae from forming.

Filtration: If you have a smaller filter that does not seem to manage your pool well enough, it may need to be replaced or turned on more often.

If you have been battling algae in a concrete pool for years, I recommend draining it and acid washing the surfaces. You might have to take drastic measures because algae can become embedded in the walls so thoroughly that you never entirely kill it with other methods. In this case, when the filtration system or chemical levels slip for just a moment, there is a new bloom.

Here are some additional details about algae prevention treatments.

Keep Your Filter Clean

If you don’t clean your pool filter regularly, it will likely clog up and not circulate water properly. It will take much longer for the algae spores to go away because not enough water is passing through the filter. In addition, there may be algae spores living in the clogged filter. Keep your filter and skimmer clean, backwash your filter, and consider changing your filtration media after dealing with an algae bloom. If you need to clean and change your filter media, head to my guides on that exact process for sand filters, DE filters, and cartridge filters.

Use Algaecide as a Preventative

Besides ultrasonic and UV technology, you can use algaecides to prevent future algae buildup. Metallic algaecides can kill off an algae bloom but are not typically used as the first line of defense. Algaecides are expensive and require large quantities to kill off substantial algae outbreaks. However, they generally perform well as preventatives.

Many products are available for killing and preventing algae growth. Routinely adding a small amount of high-quality algaecide may help prevent a problem. However, avoid overuse because these products can cause water imbalances if you add excess quantities.

BioGuard Algae All 60

I like this algaecide from BioGuard since it's copper-free, which should help prevent your swimming pool from turning a nasty green color.

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Clean Your Pool Walls

Mechanical cleaning is an integral part of keeping algae out of your pool. Brushing and vacuuming remove algae from the pool’s surfaces and make it easier for the chemicals to break down. You can also use a little bit of muriatic acid to break down algae. Algae stuck in the crevices of the swimming pool can only be removed this way.

Test Water Regularly

Inadequate sanitation and high phosphate levels are significant contributors to algae growth. These risk factors can be prevented by regularly testing your water chemistry. You can use a testing kit to check the balance of your pool water quickly.

Poolmaster 5-Way Test Kit

This is the best liquid testing kit on the market based on my testing.

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Balance Your Pool Water

If you find problems with the chemical levels in your pool water, fix them immediately. It may be tempting to let minor issues go, but this may lead to more significant problems. Fix problems with your pool water’s pH, chlorine levels, and other parameters as soon as you notice the issue.

Common Problems Caused By Algae

Algae is not only unsightly, but it can also cause many issues in your pool if left untreated. Here are some of the most common issues algae can cause in your pool.

Dangerous For Swimmers

Standard green algae is not harmful on its own. However, an algae-infested pool generally indicates that there could also be bacteria in the water, which can harm swimmers and cause skin rashes and other infections. Algae-infested water also could be caused by improper pH levels, which can irritate swimmers’ skin and eyes.

Damages Equipment

Algae-infested water can also clog your plumbing and damage your expensive pool equipment. Your pool pump may work extra hard to circulate the dirty water, which can wear out the equipment quickly.

Stains Pool Plaster And Tile

If algae is allowed to stay on your pool surfaces for some time, it may stain the plaster or pool tile. This staining can be very difficult to remove and may eventually damage the structure of the pool wall as well, which can be very expensive to fix.

Frequently Asked Questions

Can I Swim In a Pool with Algae?

Swimming in an algae-infested pool is not generally a significant risk, but I would never recommend it. For one, when you exit the pool, you will be covered in algae and probably need to shower afterward. And two, when algae grows in a pool, it generally means the chemicals are not balanced, so other more dangerous bacteria could also be in the water.

Does Pool Shock Kill Algae?

Yes, when you raise the chlorine content of your swimming pool by shocking it, the algae will die. Normal chlorine levels are not enough to kill algae, so shocking your pool is necessary to stop an outbreak.

How Do You Get Rid of Algae In a Saltwater Pool?

To get rid of algae in a saltwater pool, you should follow the same steps with a freshwater pool! Saltwater pools still need to be cleaned, shocked, and maintained, so if you find algae growing in your saltwater pool, it is time to get cleaning!

Why Does Algae In My Pool Keep Coming Back?

If algae continues to return to your swimming pool, you may have a filter that needs maintenance or replacing. Water circulation is crucial in keeping your pool sanitary. Another factor could be a chemical imbalance. I recommend checking your pH and chlorine levels at least 2-3 times a week to ensure a healthy swimming pool.

Does Phosphate Remover Kill Pool Algae?

Phosphate remover does not kill the algae in your pool. However, it prevents algae from growing as high levels of phosphates promote algae growth. If you already have algae in your pool, you should treat it with pool shock, regular brushing, and running your pump.

Are There Any Natural Remedies to Kill Pool Algae?

Sodium bicarbonate (baking soda) is a useful household item that you can use to easily kill and remove algae from the surfaces of your pool. Simply put baking soda on a pool brush and scrub the affected area. You can also use sonic wave or UV treatment to treat a small algae infestation; however, these methods are not recommended for larger amounts of algae, as they are primarily used to prevent algae growth.

You can also use bleach to resolve algae issues.

For more cleaning tips, check out my pool maintenance guide.

Questions? Shoot me a message, and I’ll be glad to help out.

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