How to Treat and Remove Algae From Your Pool

Algae can form in any pool, and it can be extremely frustrating. Many new pool owners don’t know how quickly it can grow! Although it is not usually unsafe to swim in, no one wants to swim with algae. Prevention is the best option, but if it is too late for that, there are a variety of treatment options available.

How Algae Forms in a Pool

Algae are microscopic plant cells. They are always present in the water in small quantities, but they must “bloom” in order to be visible to the human eye. This is the process where a few algae cells grow, feed, and divide, producing more and more algae cells in your pool. Algae may also be transferred in larger quantities from people or swimsuits that are contaminated by other water sources.

Most of the time, algae blooms because of inadequate sanitation, either in the form of poor filtration or improper chemical levels. It can also form because there is poor circulation in some areas of your pool. Under rails, in corners, and in other sheltered locations where treated water may not circulate properly are prime locations for algae growth.

Algae feed on almost anything, including the dead skin cells and oils leftover from swimmers. This is one reason why algae blooms may occur after a pool has gotten a lot of use. Another source of algae food is runoff from garden fertilizers, so if you have a persistent algae problem, you should investigate if water regularly gets into your pool from your garden.

Types of Algae and How They Differ

In the pool industry, the over 21,000 types of algae are usually classed into three or four groups by color. Green, black, and yellow algae are all similar but slightly different from each other in terms of treatment. Some people include pink algae, which is actually a bacterial film, and white algae, as well.

Green algae are the most common and the easiest to treat. It may form on the sides of the pool or it may be free-floating. Green pools occur when enough free-floating algae of this type are present in the water. It’s often caused by a lack of proper sanitation but can be removed by a chlorine chemical shock.

Yellow algae, which is also called mustard algae or brown algae, tend to occur on sheltered surfaces. This may be the floor or the walls of your pool making it harder to get rid of than green algae. To remove yellow algae, shock your pool with twice the amount of chlorine you would use for a typical shock treatment. Run the pump and filter for 24 hours after brushing the walls and floors aggressively.

Black algae usually show up as spots on the walls, and it is extremely persistent but relatively rare. Black algae have a hard outer shell that protects the cells inside. Removal can be difficult, but not impossible. To remove black algae from your pool, scrape as much as you can off the walls and shock your pool with three times the amount of chlorine you would use for a typical shock treatment.

Pink slime is not an algae at all, but is often misconstrued as pink algae. Pink slime is a bacteria and forms as a slimy pink or clear layer over the pool’s surface. It is a bacteria so regular brushing and vacuuming can decrease the chance of pink algae. If your pool does start forming pink slime, chemical shock your pool and leave the filter on for 24 hours.

How to Use Chemical Treatments to Remove Algae

There are two major chemical treatments for algae: chlorine and flocculant.

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

How the filter is used depends on the chemical choice you make. If you add floc, you should run the filter in a recirculating mode or not run it at all, for a few hours. Then, you must turn it off to give the algae time to settle. If you use chlorine shock, you should run the filter almost continuously. Check regularly to make sure that the filter does not become clogged with algae.

How to Use Chlorine Shock to Remove Algae

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

  1. Vacuum your pool. Make sure to use a manual vacuum so you bypass your filter to go directly to the waste. The last thing you want is to recirculate the algae throughout your system.
  2. Brush your pool walls. This includes the floor too. Getting most of the hard work done with ensure your sanitizer can get to the hard to reach algae to clean everything thoroughly. 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, which will make sure your sanitizer will be as effective as possible.
  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. For green algae, multiply the shock package instructions by 2 for the size of your pool. For mustard algae, multiply by 3. For black algae, multiply by 4.
  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 not sure what to use, head over 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 about 6 hours or more to make sure all the algae filters out of the system and your water turns from a cloudy blue to crystal clear. After waiting, test the water again for proper chemistry levels before going swimming.

How to Use Flocculant to Remove Algae

​​Flocculant, or floc, is a chemical and mechanical process that works fast. It clears severely 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.

  1. Raise the water level in your pool because you will vacuum a lot of water out.
  2. Dilute the flocculant in a bucket by following the directions on the container.
  3. Pour the diluted flocculant around your pool near the pool walls.
  4. Allow the floc to disperse around the pool by circulating the water for two hours.
  5. After shutting your pump off, the floc will bind to the algae and settle on the pool floor. Let it sit overnight if possible.
  6. Turn the multi-port valve to waste. This will ensure dirty water doesn’t get back into your pool.
  7. Start vacuuming the pool, working slowly to make sure you get all the thick sediment off the floor.
  8. Add replacement water while vacuuming.
  9. Run your filter until the water clears.

How to Get Rid of Algae with Non-Chemical Treatments

There are two major types of non-chemical solutions for algae, but both are aimed more at preventing algae blooms than dealing with one that is already in progress. Still, if you have a minor algae problem, you might be able to use one of these devices. You would need to first re-balance the water as normal, 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 mechanically clean it. These devices are extremely effective at killing algae that comes through them. However, they are physical processes, not chemical ones, so they have no effect on algae cells that do not actually pass through the system. For this reason, they are much more effective preventative measures than treatment ones.

Read our full guide on how to clear green pool water to learn more!

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Tips to Prevent Swimming Pool Algae from Coming Back

Swimming pool algae can be a frustrating problem, and the last thing that you want after you finally get it under control is for it to come back. Luckily, algae is easier to prevent than it is to get rid of (even for saltwater pools turning green), so the hard part is already done. To avoid a future headache, invest a little time to work on preventing algae blooms.

The main preventative treatment for algae is to improve the sanitation, circulation, and filtration in your pool. If you have a filter that is only just big enough for your pool, it may need to be run more or replaced with a larger one. Maintaining balanced water levels is also extremely important. If you have been battling algae for years in a plaster pool, it may be time to drain it and acid wash the surfaces. This is because algae can become embedded in the walls so thoroughly that you never really kill it all with other methods. Then, when the filtration system or chemical levels slip for just a moment, there is a new bloom. Here are some additional details about each of these treatments.

Keep Your Filter Clean

If your pool filter is not cleaned regularly, it will likely become clogged and will not circulate water as well as it should. Algae spores in the water will not be removed at a high enough rate because not enough water is passing through the filter. In addition, clogged filtration material may actually harbor algae spores. Keep your filter and skimmer clean, backwash it, and consider changing your filtration media after dealing with an algae bloom.

Use Algaecide as a Preventative

Aside from sonic and UV technology, there are algaecides that can be used to prevent future algae buildup. Metallic algaecides do have some ability to kill off an algae bloom, but they are not usually the first line of treatment because they are expensive and otherwise not ideal in the quantities required to kill an active problem. As preventatives, they usually do a good job.

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

Clean Your Pool Walls

Mechanical cleaning is an important part of keeping algae out of your pool. Brushing and vacuuming remove algae from the pool surface and puts it into suspension in the water. Algae stuck in the crevices of rough plaster may not be able to be removed any other way.

Test Water Regularly

Inadequate sanitation and high phosphate levels are major contributors to algae growth. Both of these risk factors can be tested for and treated as necessary. Regular testing of your water chemistry allows you to catch these problems when they are only a minor issue and easy to fix. You can use a water test kit to easily see how out of balance your pool water is.

Balance Your Pool Water

If you find that there are problems with the chemical levels in your pool water, fix them right away. It may be tempting to let minor issues go, but this may lead to bigger problems. The time to fix problems with the pH, chlorine levels, and other parameters of your pool water is as soon as you notice the issue.

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

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