How to Get Rid Of Black Algae

Black algae is perhaps the hardest algae to get rid of. Follow this step-by-step guide to help you get rid of black algae in your pool fast.



Black algae is perhaps the hardest algae to get rid of. It has very deep roots that can grow into the side of plaster or concrete pools. It also has many layers that protect it from normal chlorine levels. You will usually find black algae clinging to your pool walls or steps in very shady spots. So in order to get rid of this algae, you must be aggressive!





Black algae comes from the ocean. A common way for you pool to be infected by black algae is by a bathing suit that has once been in the ocean.

With that said, always wash your bathing suits after swimming. It’s just good practice.

Here is a step by step guide to get rid of this slimy, stubborn creature.

Warning: Be prepared to do a lot of brushing. I suggest buying a good quality brush for this procedure.












1. Sanitize everything

Bathing suits, equipment, toys, and floats. Make sure you wash your bathing suits in a washing machine and dryer. This should kill the algae. Wipe down toys and floats with Clorox cleaner. Use a scrub brush for more thorough cleaning. Keep all the maintenance equipment in the pool so that it becomes sanitized.


2. Check the water chemistry in your pool

Make sure your pH levels are between 7.4 and 7.6 and your alkalinity levels are between 120 and 150 ppm (parts per million).













I cannot stress this enough. This will be the key to getting rid of black algae. Brush hard, brush thorough, brush often. Black algae forms a membrane which needs to be broken for treatment to work.

Brush the walls and floors with a steel bristled brush or a stiff plastic bristled brush for plaster pools


4. Triple shock your pool

Add 1.5kg for every 40,000L of water your pool holds. Make sure you add the shock at night or dusk and run your filter 24 hours a day until the black algae has been taken care of.

Leave filtration off for 24 hours to allow treatment to attack the blackspot.












5. Brush your pool again and again

Brush it the following day at least 3 or 4 times concentrating on where you first spotted the algae. Remember, black algae has deep roots that can be embedded into your pool walls. It may look like it’s gone, but it’s probably still in there. Just keep brushing. Continue brushing for several days after the shock. I would wait about 3 days and then shock your pool again with a normal amount. 500g per 40,000L of water. Brush for a few more days after that until you feel confident that the black algae is gone.

This is not a guarantee. Black algae is a bastard and could continue to infect your water. If it does, you know how to kill it, just be more aggressive next time. Perhaps an additional dose of triple shock and constant brushing.


6. Vacuum any waste

To prevent any spores reticulating into the filtration vacuum to waste any debris on the floor of the pool.












7. Clean your filter

At the completion of your water treatment, thoroughly clean your filter. This includes manually washing your cartridge filter or backwashing your sand filter.



Keeping your pool properly balanced and sanitized is the key to keeping all forms of algae from growing. Make sure you

  • Keep your pH, alkalinity and sanitizer levels in the correct range at all times.
  • Run your pump and filter for 8 to 12 hours a day all season long.
  • Keep your pool clean by regularly vacuuming and brushing
  • Shock your pool every week. 500g per 40,000L
  • Keep your additional pool equipment clean including pool toys, floats, ladders, steps, diving boards, slides, solar blankets and covers.


Happy Swimming!

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