Algae Troubleshooting Guidance

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.



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.

  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, the following factors need to be considered before treatment:


It is critical that sufficient algaecide is added to treat all of the algae at one time. The use of only some of the needed algaecide will not kill some of the algae. It is important to follow the directions for use on the package.

Swimming Pool Green Algae


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


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

Different types of algae require different types of treatment.


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.


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.

Swimming Pool Yellow 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 gain 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 continue 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.

The following steps will help in bringing black algae under control:

  • Correct any problems with the circulation pattern in the pool.
  • Brush the colonies as this will break through the waxy coating protecting the colony. This is an important step!
  • Add an algaecide intended for use on black algae.
  • Brush the colony daily thereafter, if possible, as this will remove any dead cells from the surface exposing the living cells underneath for exposure to the algaecide.

Following these simple procedures when treating Black Algae will not only help ensure its successful removal but reduce the likelihood of its return as well.

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