Just woke up to a green pool? Finding algae growing in your pool can be highly frustrating. Many new pool owners don’t realize how fast it can grow. Although it is not entirely unsafe, nobody wants to swim in green water! There are many ways to prevent algae from growing, and there are also some treatment options if it has already started growing. But first, let’s cover how algae forms and the types of algae in swimming pools, which is important to know how to treat it. If you’ve already identified the algae in your pool, feel free to jump right to my steps to clean it up.
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 or swimsuits that are contaminated by other water sources.
Most of the time, algae blooms because of inadequate sanitation due to either poor filtration or improper chemical levels. It can also form because there is poor circulation in some areas of your swimming pool. 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. They 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 pretty similar but have slight differences in terms of 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 is the most commonly found algae and also the easiest to treat. It may form on the sides of the pool, or it may be free-floating (example below for what it looks like). Green pools occur when enough free-floating algae 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 recommend using double the average quantity for the chemical shock.
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 usually shows up as spots on the walls, and it is highly persistent but relatively rare (image below with an example). Black algae have a hard outer shell that protects the cells inside, making removal very difficult, but not impossible. To remove black algae from your pool, scrape your swimming pool walls vigorously and shock your pool with four times the amount of chlorine you would use for a typical shock treatment.
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.
- 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.
- 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.
- 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.
- Wait until the right time. Chlorine reacts to sunlight, so it’s best to wait until the sun goes down before shocking your pool.
- 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.
- 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 over to my guide on the best pool shock.
- 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.
- 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 going swimming. Make sure you check and adjust your pH, alkalinity, chlorine, cyanuric acid, and calcium hardness levels as needed.
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. For getting rid of little green algae quickly, I recommend using floc with the following steps.
- Raise the water level in your pool. A necessary step as you will end up vacuuming a lot of water out.
- 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.
- 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.
- 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.
- Turn the multiport valve to waste. The waste setting will ensure dirty water doesn’t filter back into your pool.
- Vacuum the pool. Remove all of the sediment that has collected at the bottom of the pool.
- Add more water. After vacuuming, you will need to add replacement water.
- Run your filter. Let your filter run until the water clears up and all the dead algae is removed.
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 would need to 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 that 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 our full 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.
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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 they 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.
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 makes it easier for the chemicals to break down. Algae stuck in the crevices of the swimming pool can only be removed in 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.
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.
Frequently Asked Questions
Can I Swim In a Pool with Algae?
It is not generally a significant risk to swim in an algae-infested pool, but I would never recommend it. For one, when you exit the pool, you will be covered in algae and will probably need to take a shower afterward. And two, when algae grows in a pool, it generally means the chemicals are not balanced, so there could also be other more dangerous bacteria 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.
For more cleaning tips, check out my pool maintenance guide.
Questions? Shoot me a message, and I’ll be glad to help out.