How do you get rid of Pool Algae?

Algae growth is perhaps the most obvious sign of something gone wrong with pool maintenance. Proper maintenance will not only keep your water looking great, but also allow for easy prevention of algae growth. When preventative measures aren’t enough, you’ll need to remove the algae to get back to enjoying your swimming pool.

Before we explore how exactly to clear your pool of pesky algae, let’s discuss the most common types of algae:

There are two basic groups of algae:

1. Free-floating types including green and mustard varieties. These tend to be found throughout the water. Mustard algae tends to cling loosely to the walls of the pool and brushes off easily. It tends to have a yellowish color. Green algae will be visible throughout the water itself and will turn the water different shades of green depending on the infestation.
2. Black algae is the common name or term given to the dark blue-green algae found growing on pool surfaces. Black algae grows in localized areas such as along one wall, in the deep end, in a corner or around obstacles such as steps indicates an area of poor circulation and poor sanitization.

The growth of both types of algae can be easily prevented by using a quality algaecide as part of a regular maintenance program, and by proper circulation. It takes far less algaecide to prevent algae growth from getting started than it will to cure it once it has occurred.

The regular use of algaecide is also recommended to prevent problems should a failure of the sanitization program occur. Due to the unique nature of chlorine or bromine, these residuals can often be lost very quickly in pools due to equipment or operator error or by heavy rainfall or bather waste demand. Improper water balance will contribute to the ability of your sanitizer to work properly and prevent algae growth. If this occurs without an algaecide present, the rapid growth of algae can occur in a few hours. However, if an algaecide is present, it will act as algae growth prevention (look at it as an insurance program) until the sanitizer system is functioning normally.

In spite of your best efforts, algae problems can occur and require some consideration for proper treatment. When an algaecide becomes necessary, read our guide to pool algaecide types to find your perfect product.

Age of the Algae

The older algae becomes, the more difficult it is to control. Treat the problem as soon as it is noticed.

Sunlight and Water Temperature

It is best to treat when algae are actively growing. Sunny days and a water temperature of 60°F or higher will be helpful.

Type of Algae

How to Get Rid of the Different Types of Algae

Different types of algae require different types of treatment.

Green Algae

The most common algae associated with swimming pools is green algae. It is very opportunistic, meaning it will take advantage of any failure in the normal sanitizing program and quickly infest a pool. One will see green algae problems frequently appear overnight following heavy rainstorms. This is because rainstorms actually provide food for the algae in the form of nitrogen. The nitrogen not only feeds the algae but also destroys chlorine residuals.

Green algae must not be mistaken for metal present in the pool water. Metals, especially copper, can give the water a clear green tint. The best way to treat green algae is to prevent it in the first place. Use an algaecide regularly as part of a normal maintenance program. This will prevent algae from growing, even if a failure in the sanitizing system was to occur. It is always easier and more effective to prevent the algae problem than to try and eliminate it once it occurs. When it does occur, treat it promptly. The longer you wait before treatment, the more difficult and costly the result. Select an algaecide that will both kill the existing algae and prevent renewed growth. Follow the label directions and maintain circulation during treatment.

How to get rid of green algae:

1. Test your pool water. Add chemicals as needed to ensure that your pool water is balanced before you start the algae removal process.
2. Shock your pool with a chlorine shock treatment. Run your filter for at least 24 hours after you add the shock treatment.
3. Scrub away the green algae. Use a pool brush to scrub the algae off of your pool walls.
4. Add algaecide. Most pool supply retailers sell algaecides that are specially formulated to remove green algae.
5. Scrub (again) and vacuum. Take a second pass with your pool brush to remove any remaining green algae. Follow up by vacuuming your pool. This will remove any dead algae that has collected at the bottom of the pool.

Yellow or Mustard Algae

Yellow or mustard algae is very similar in form to green algae, but is much slower growing and is deficient in chlorophyll (green pigment) which accounts for its yellow color. It is easily identified by the ability to brush it easily off the pool walls and floor. Because yellow algae grow very slowly, it is also very difficult to destroy. By the time you see it growing in your pool, it has likely been there as long as several weeks. Additionally, since yellow algae is low in chlorophyll which is light-loving, the algae live and even grow in dark areas of the pool such as plumbing and filters. This only compounds the difficulty of control.

To treat mustard algae, care in selection of a proper algaecide is most important. Be certain to select a product made for the control of this unique form of algae. Copper-based algaecides seem particularly well suited for controlling yellow algae. One word of caution: it is not unusual to need to treat yellow algae more than once to bring it fully under control. This again points out the value of preventing the growth in the first place.

How to get rid of mustard algae:

Clean everything that has come into contact with your pool water. Wash swimsuits and towels (use bleach!), and make sure to clean and disinfect pool toys and equipment. Remember, yellow algae spores can survive on almost any surface, so this step is critical!

1. Scrub and vacuum your pool. Use a good pool brush to scrape yellow algae off of your pool walls. Once you’ve removed all of the algae, vacuum your pool thoroughly.
2. Test and the water. If anything is out of balance – say, the pH is too high or the alkalinity is too low – add chemicals to bring things into line.
3. Brush the pool (again). This will help ensure that you get any remaining algae.
4. Shock your pool. You'll need to use around three times more shock treatment than you'd use for green algae. Run your pool filter for at least 24 hours to ensure that the shock treatment can circulate.
5. Repeat steps 3, 4, and 5 as needed. Test, brush, and shock your pool as needed, until your pool is 100% algae-free and your water chemistry is balanced.

Black Algae

Frequently considered the most difficult algae to control is the one we commonly refer to as "black algae". However, it is also likely the easiest to prevent. Black algae typically gains a foothold in areas of the pool that suffer from poor circulation. Areas such as corners, or in certain areas of the deep end, are often identified as places where black algae continues to show up in a particular pool and are then nearly impossible to eliminate. Most often, these areas suffer from inadequate circulation and thus little or no fresh water, sanitizer or algaecide gets to the area with any regularity.

One of the best ways to prevent black algae growth or eliminate it once it surfaces is to correct the circulation problem(s) first. Once it begins forming, black algae develops specialized cells that lock it deep in the pores of pool surfaces. In order to effectively control it, all of its cells, including those deep in the surface, must be killed. It is all but impossible for chlorine alone to get this deep into the pores of the pool.

In addition to the attaching or locking mechanism of black algae, the growing colony also produces a defense mechanism. Outer layers of the colony produce a waxy coat that prevents chlorine or algaecides from penetrating into the colony and killing it. Therefore, the algaecide used should contain a "penetrating" agent. This agent will actually work to help the algaecide penetrate into the pores of the pool surface and cut through the waxy coat with a special wetting action that chlorine does not have.

How to get rid of black algae:

1. Clean your filter. Chances are good that if your pool has black algae, your filter probably has it, too.
2. Scrub the black algae away with a good, stiff pool brush. This will help break down the protective layer and make it easier to treat.
3. Break a chlorine tablet in half and rub it directly onto the affected areas. The chlorine treatment will kill the algae’s roots and prevent it from coming back.
4. Shock your pool. Because black algae is tougher than other types of algae, you might need to use a stronger dose of pool shock. Check the directions on the package or talk to your local pool supply retailer.
5. Add algaecide to your pool. This will help keep the black algae from growing back.
6. Run your pool filter. Keep it running for at least 24 hours to ensure that the treatments and chemicals can circulate properly.
7. Test your pool water. Keeping your water chemistry balanced can help prevent future outbreaks.

Any time algae develops in your swimming pool, it is best to consult your professional pool retail provider for the best solution available.

Pink Algae

Like black algae, this reddish-pink growth isn’t a true algae. It’s actually a type of bacteria – in this case, a slimy bacteria that thrives around PVC pipes and in shady spots on your pool’s surface. Like all other types of algae, pink slime is totally harmless. Unlike black algae, pink algae lacks a protective shell, so it isn’t especially tough to remove.

How to get rid of pink algae

1. Scrub all of the pink algae away with a pool brush.
2. Use an intense chlorine shock treatment (4 pounds per 10,000 gallons). Since it’s not truly a type of algae, you’ll need to use a higher dose to kill off pink algae.
3. Run your pool filter for 24 hours.
4. Test your pool water to ensure the chemicals are balanced.

Swimming Pool Algae FAQs