Black Algae In a Pool: What It is, How to Remove & Prevent

Black Algae In a Pool


Black algae take the top spot for the most dreaded infestation that can happen to your pool, and for a reason; they are hard to get rid of.

This article explains what black algae are, and gives a step by step guide on how to remove it from your pool. It also highlights how to prevent black algae infestation in your pool, altogether.

What are Black Algae? 

Black algae manifest as black spots that grow on the rough surfaces of your pool. Although they are single-celled organisms, they appear in clusters. They continue to multiply over time if you do not act fast and get rid of them.

They have major similarities with other green algae but they appear black. This can be attributed to the fact that although they contain chlorophyll (green color), they have a layer that masks it.

They have roots that attach to the cracks and crevices on the surface of the pool making them hard to get rid of. Additionally, they are resistant to normal chlorine levels in a pool.

Why are Black Algae Bad for Your Pool? 

While most people worry about the unsightly appearance of the algae that makes the pool unpleasant to swim in, black algae in large numbers can cause blockage of the pool filter, rendering it ineffective.

Additionally, the dark color of black algae protects bacteria such as E.Coli and infectious Salmonella strains from the sun’s UV rays. The harmful bacteria attach to the black algae and the dark environment allows them to thrive and multiply in your pool.

These bacteria cause stomach illness such as typhoid fever and nausea when a swimmer swallows the pool water, which is not unlikely.

How to Remove Black Algae from Your Pool

How to Remove Black Algae from Your Pool


1. Sanitize Pool Accessories 

Most times, black algae are introduced into a pool by unsanitary swimming accessories that have been used in natural water bodies such as the ocean or lakes.

Therefore, you will need to sanitize your pool accessories such as swimsuits, swimming goggles, swim caps, toys, floats, etc.

This will ensure that once you get rid of the black algae from the pool, these accessories will not reintroduce them.

2. Test and Balance the Pool Water  

When your pool pH level is neutral and the total alkalinity level is optimal, black algae will not survive.

This balance can be tested using a pool water testing kit; this takes away the complexity of guessing or improvisation. The test kits are either in liquid form or test strips, and you can choose according to your preference.

You will, therefore, need to test your pool water regularly and maintain a neutral pH of between 7.1 and 7.6.

Read More: The Best pH Meters

If the pH is below 7.1, you raise it by adding alkaline to create a base environment. If the pH is above 7.6, you balance it by adding an acid.

3. Scrub Your Pool

Black algae do not float around in the pool. Instead, they attach to the rough surfaces on the pool edges. This makes it even more difficult to scrub off.

This requires a lot of elbow grease and is the step that will probably take up much of your time and energy.

Not to worry though, special algae scrubbers are available and are easier to use because regular pool brushes may not be effective to remove black algae.

For tiled and concrete pool surfaces, use a stainless-steel bristle brush to access the crevices and effectively remove the black algae.

This is pretty easy to do as the brush does not require much force to remove the algae. You may also use a putty knife or pumice stone for surfaces that the brush cannot reach.

However, for pools with vinyl liners or fiberglass, use a nylon-bristled brush. This is important to note as using the stainless-steel bristle brush may scratch these pool surfaces and provide more crevices for black algae to attach.

Once the black algae detach from the surface, they will be easy to kill when you shock the pool.

4. Clean Your Pool Filter

When your pool has been infested with black algae, it most definitely has reached the pool filter.

To avoid re-infestation of the pool by the black algae after cleaning the pool, it is important to clean the pool filter thoroughly.

Plain water and home cleaning agents may not be effective for black algae though. Therefore, it is advisable to use a pool filter cleaner to ensure that no black algae spots are left on its surface.

You should consider replacing the pool filter on the occasion that the black algae infestation is very high or difficult to clean. This, however, should be considered as a last resort.

5. Shock Your Pool

Pool shocking is meant to ensure that the detached black algae are killed and, therefore, prevent re-infestation of the pool by the black algae. To get rid of black algae, it should be done using chlorine shocks at 2-6 lbs. of pool shock per 10,000 gallons of water.

It is advisable to wear protective gear while handling the pool shock reagents. You should also avoid using the pool right after shocking because the shock concentration is very high and may harm your skin.

To aid in the circulation, pour the shock close to the pool jets then run the pool pump for at least 24 hours. You may also place your pool accessories in the pool during this process to kill any black algae that may have been left on them during the sanitization process.

Pool shocking is best done in cloudy weather or at dusk because the sun is known to reduce the effectiveness of the pool shock.

Regular pool shocking is recommended weekly or whenever necessary. It is advisable to always consult the shock’s package label for any other specifications. To learn more about when to shock your pool, refer to this article.

How to Prevent Black Algae

How to Prevent Black Algae


  • Ensure that all pool accessories are thoroughly cleaned before they are used in your pool. Special sanitization must be carried out especially if they have been used in natural water bodies such as lakes.
  • You should rinse off before using the pool, especially if you have been swimming in a natural water body.
  • Ensure that your pool water is well balanced to make sure black algae do not thrive in it. Check pool pH and alkalinity levels regularly and correct them whenever necessary.
  • Brush your pool regularly and keep it clean. Pay special attention to rough surfaces on the edge of the pool.
  • Run the pool pump and filter for at least 8 hours daily to aid in water circulation. This prevents water stagnation which otherwise encourages algae to thrive in your pool.


In conclusion, the best way to prevent black algae in your pool is by maintaining hygiene in your pool and pool accessories.

However, in the unfortunate event of its infestation, sanitize your pool accessories, test and balance your pool water, scrub the black algae off the surfaces, clean the pool filter and finally, shock your pool to kill the black algae.