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Black Algae in Swimming Pools: How to Identify and Treat It

Black Algae in Swimming Pools: How to Identify and Treat It

Swimming pools are a great addition to any home, but they also require proper maintenance and care to keep them clean and safe for swimming. One of the most common problems that pool owners face is algae growth, with black algae being one of the most stubborn and challenging types to treat. In this article, we will discuss what black algae is, how to identify it, and the steps to take to eliminate it.

What is Black Algae?

Black algae, also known as blue-green algae or cyanobacteria, is a type of algae that can grow in swimming pools. It typically appears as black or dark blue-green spots on the pool walls, steps, and other surfaces. Unlike other types of algae, black algae are very resistant to normal pool sanitation methods, including chlorine. It can also grow deep into the pool surfaces, making it difficult to eliminate.

Identifying Black Algae

The first step in treating black algae is identifying it. Black algae typically appear as black or dark blue-green spots on the pool walls, steps, and other surfaces. These spots can be hard and slimy to the touch and may appear as a rough or raised surface. Unlike other types of algae, black algae tend to cling stubbornly to surfaces and are not easily brushed off. It also tends to reappear quickly after treatment, which is a sign that it’s not other types of algae or dirt.

Treating Black Algae

Treating black algae requires a persistent approach, as it can be challenging to eliminate. Here are the steps you can take to eliminate it:

  1. Brush the pool: Use a pool brush to vigorously scrub the affected areas to loosen the algae from the surface. Be sure to brush all the surfaces of the pool, including steps and corners.
  2. Shock the pool: Use a pool shock treatment that contains a high level of chlorine to kill the algae. Follow the instructions on the package carefully. Be sure to maintain the pool’s chlorine levels for several days to prevent the algae from regrowing.
  3. Use a specific algaecide: Use an algaecide designed specifically to combat black algae. Follow the instructions on the package carefully. Algaecides should be added after shocking the pool to prevent their interaction with the shock treatment.
  4. Scrub the pool: After adding the algaecide, use a stiff-bristled brush to scrub the affected areas once again. This will help to remove any remaining algae and prevent it from regrowing.
  5. Vacuum the pool: Once the algae has been eliminated, vacuum the pool thoroughly, paying close attention to the affected areas.
  6. Maintain the pool: Once the algae has been eliminated, continue to maintain the pool with proper chemical balances, regular brushing, and vacuuming to prevent the algae from returning.

It’s important to note that black algae can be difficult to get rid of, and may require multiple treatments. It’s also recommended to consult with a pool professional for guidance on proper treatment and prevention.

Preventing Black Algae

Prevention is the key to avoiding black algae growth in your pool. Here are some tips to keep your pool clean and healthy:

  1. Maintain proper chemical balance: Regularly test the pool’s pH, alkalinity, and chlorine levels to ensure that they are in their recommended range. Adjust them as necessary to keep the pool water healthy and clean.
  2. Clean and brush regularly: Regularly brush and vacuum the pool to remove dirt and debris that can promote algae growth.
  3. Ensure proper circulation: Ensure that your pool’s pump and filter system are working properly, and that water is circulating properly in all areas of the pool.
  4. Use a pool cover: Use a pool cover to prevent debris and other contaminants from entering the pool when it’s not in use. This can help reduce the risk of algae growth.
  5. Limit sunlight exposure: Algae grow best in direct sunlight, so consider planting trees or adding umbrellas to shade your pool.
  6. Regularly shock the pool: Shocking the pool with a high level of chlorine can help prevent algae growth by killing any algae spores before they have a chance to take hold.


Black algae can be a challenging problem for pool owners, but with persistence and proper treatment, it can be eliminated. Identifying black algae early and taking steps to treat it immediately is crucial to keeping your pool clean and healthy. Regular maintenance, proper chemical balance, and prevention measures can help prevent black algae from growing in the first place. By following these steps and consulting with a pool professional when necessary, you can ensure that your pool remains a safe and enjoyable place to swim for you and your family.

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