Black Algae Guide

Black Algae — The Toughest Pool Problem

Black algae is far more stubborn than green algae. It forms a protective waxy layer that resists standard treatments and sends roots deep into plaster and grout. Once it takes hold, it keeps coming back — unless you treat it correctly.

Common causes

  • Contaminated pool equipment or swimwear
  • Poor circulation in corners and steps
  • Rough or plastered pool surfaces where roots can anchor
  • Infrequent or inconsistent treatment
  • Lightning storms disrupting water balance

Signs you have black algae

  • Dark blue-green or black spots on pool walls and floor
  • Spots that return even after brushing
  • Rough texture on plaster surfaces

How to treat black algae with Activator-D™

  1. Backwash your filter before treatment.
  2. Brush affected areas vigorously to break through the waxy protective layer.
  3. Pour the Activator-D Powder directly into the skimmer/weir.
  4. Pour the Activator-D Liquid into the skimmer/weir immediately afterwards.
  5. Run the pump continuously for 8–12 hours.
  6. Re-brush any remaining spots and allow the filter to remove dead algae.
  7. Vacuum dead algae to waste.

Tips for best results

  • Clean your filter thoroughly — black algae spores can survive in dirty filters.
  • Run the pump overnight if possible.
  • Apply Activator-D™ every month to prevent regrowth.

Black algae can take 48–72 hours to fully clear depending on severity. Consistent monthly treatment is the best prevention.

Activator-D™ is a chlorine-free monthly treatment specifically formulated to penetrate the protective layer of black algae and eliminate it at the root — keeping your pool clear all year round.

 

Need Help Choosing the Right Activator-D Pack?

Whether you're treating a green pool, black algae, or maintaining crystal-clear water every month, Activator-D makes pool care simple.

Shop the Activator-D 1 Pack, 4 Pack or 10 Pack and enjoy fast delivery anywhere in South Africa.