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Black algae is a stubborn growth in the pool that is both dangerous and unpleasant to look at. It can leave black stains all over the pool floor, walls, and steps, which can take a lot of elbow grease to finally remove.

If you notice blue-green spots on your pool surface, it’s time to be proactive! These spots are early indications of black algae growing in your pool. The sooner you attack it, the sooner it will be gone, and the less likely it is to stain the pool permanently.

If you want to know the best way to get rid of algae in your poo, keep reading.

What’s the Best Way to Get Rid of Black Algae in a Pool? 

It’s very important to thoroughly scrub your pool surfaces and shock your pool several times to fully eradicate black algae. You must get rid of black algae clinging to the walls, stairs, floor, in your skimmer, and anywhere else it might be hiding to avoid it from surviving shock treatment.

Follow this step-by-step guide to clean your pool of this particularly resilient bacteria successfully:

  1. Brush the pool walls with a nylon brush or steel bristle brush
  2. Continue scrubbing until you don’t see any black algae clinging anywhere
  3. Scrub the skimmer, skimmer basket, and backwash your pool filter
  4. If you have a cartridge filter, use a filter cleaner to flush out the bacteria thoroughly
  5. Once all the black algae are loosened from the walls, shock your pool water
  6. Check the manufacturer’s directions to determine what one dose equals and quadruple shock the pool (multiply one dose by four)
  7. Always add shock in the evening or at sunset to avoid having the sun destroy the chlorine’s molecular bonds
  8. Run the pump all night to keep the chemicals moving in the swimming pool
  9. The next day the water might be cloudy due to the chemical levels, but you should see little to no remaining black algae
  10. Scrub the walls and floor again with the pool brush to loosen any remaining algae particles and spores
  11. After a day check your pool for more algae spores or clinging particles
  12. If you want to be on the safe side, add a double dose of shock to your pool water
  13. Continue scrubbing your pool and running the pump until you see no more black algae
  14. Backwash or clean your filter medium

There’s no need to replace the filter medium so long as you backwash or clean your filter cartridge. The black algae should all be killed thanks to the shock treatments, but backwashing will ensure all the particles are flushed out.

What is Black Algae in Pools? 

Black algae growth usually begins in small crevices of the swimming pool. It lodges in the pores of concrete, tile, and pool liners. Even the smallest crevices are enough to allow the spores to take root and grow.

Black algae look very similar to black mold in houses, but it’s not the same thing. Black algae aren’t even algae!

Black algae is a form of cyanobacteria that spreads through cross-contamination from one body of water to another. Cyanobacteria is a form of bacteria that photosynthesizes to feed and energizes itself to reproduce.

Cyanobacteria is over 3 million years old and predates all algae, plants, and other aquatic plants that require photosynthesis. That’s because cyanobacteria were the original photosynthesizer thanks to these ancient bacteria plants that absorb sunlight today.

Green algae are distantly related but have a much more recent evolution. Given that black algae existed for so long, you can imagine how resilient this pesky growth can be in your swimming pool. While it’s resilient and difficult to eradicate from the water, it’s not impossible.

Why Does Black Algae Grow In a Swimming Pool? 

Imbalanced pool water makes swimming pools an appealing breeding ground for black algae. However, black algae usually only grow in a natural body of water, not a swimming pool. Unlike green algae that can spread from organic matter falling into your swimming pool, black algae need to be transferred.

The most likely cause of black algae entering your pool water is contamination. Most likely, you or one of the people using your pool went swimming in a natural body of water recently. The black algae can cling to a piece of clothing or a bathing suit and be transferred to your pool water.

Black algae can enter your pool water if you don’t clean your bathing suit or clothes properly after swimming in a lake, river, or ocean. Use bleach or color-safe bleach to clean your swimwear after swimming in natural bodies of water to kill black algae.

However, once you get black algae in your pool, you’ll need to sanitize and scrub your pool until it’s totally clean.

Can You Kill Black Algae Naturally? 

There aren’t any natural alternatives to kill black algae in swimming pools. You must use a chlorine-based shock, or a sodium hypochlorite shock treatment to kill black algae in your pool and pool pump.

However, you can use baking soda or borax to spot-clean your pool walls and remove tough growth and stains. If your pool’s walls are concrete, you can use a stainless steel brush and borax to clean off hardened black algae along the water’s edge.

Borax and baking soda aren’t effective in killing algae in your pool. They’re not considered a sanitizer like chlorine or bromine, but they’re effective at exfoliating surfaces and removing spores from pool surfaces.

After shocking your pool and killing the black algae growth, use borax or baking soda to scrape away lingering particles or stains. You can also use chlorine tablets to scrape stains from the pool surface.

While this won’t kill algae in your pool, they’re great for removing stains!


Getting rid of black algae can be difficult but not impossible. We hope this guide took you one step closer to removing this unpleasant and dangerous bacteria from your pool’s water.

Ensure you clean your pool pump with filter cleaner and sanitize all of your pool equipment. This will guarantee that all the bacteria and algae in your pool are killed and gone permanently so it doesn’t come back!

Next, balance your pool water chemistry to ensure you don’t get more growth in the future. If you want to learn more about balancinge your pool’s chemical levels, check out our article on the topic!


Can Black Algae Hurt Swimmers? 

If you’re wondering, “Is black algae harmful?” the short answer is yes. Unlike green algae or yellow algae in your pool, black algae are dangerous. This is because black algae is a bacteria that can cause serious digestive discomfort.

This is especially true if you accidentally swallow some of the water and consume black algae. Black algae are harmful and you should avoid letting anyone swim in the pool until you get rid of it!

Can Black Algae Damage Your Pool? 

Black algae won’t cause serious damage to your pool or pool pump. However, it can be corrosive over extended periods and can leave ugly stains on your walls, floor, and steps. The best way to prevent any permanent damage to your pool is to get rid of the black algae as soon as possible.

Is Black Algae the Same as Blue-Green Algae?

Blue-green spots on your pool surfaces are a key component for you to identify black algae growing in your pool. Black algae actually only look black on the tip of the growth of the algae.

Black alga is a blue-green color, but when the hard outer shell becomes a dark, black color. This is why this algae in your pool look black and is often referred to as black algae.