Black algae can be a problem for aquarists and pool owners alike. Black algae will form small (typically 1-3 cm / 0.4-1.2 inches in diameter) black or dark blue green dots on various surfaces, such as aquarium glass and pool sides. You can find similar algae on shower tiles and silicone seems in moist bathrooms. Just like the dreaded yellow algae, black algae are capable of blooming even in pools with proper filtration and plenty of chlorine.
Black algae will form layers where the surface layer protects the underlying layers. Washing with chlorine will typically only kill the outer layer and getting rid of black algae can be really tricky. The black algae have strong roots planted firmly in the surface and you have to destroy the roots if you want to completely eradicate the algae. If any roots are left, new black algae will become visible in the same spot sooner or later. On the good side, black algae grow extremely slowly compared to most other types of algae.
Even though black algae grow slowly, it is best to fix the problem as soon as you notice it. The longer you wait, the harder it will be.
How to get rid of black algae
Which method to use when destroying black algae will naturally depend on whether it is present in a pool, in a bathroom, in an inhabited aquarium or in an uninhabited aquarium. This method below is commonly used to rid pools of black algae.
- Check the pH-value of the water and adjust if necessary.
- Make sure that the filtration functions properly.
- Check filter pressure.
- Backwash if necessary.
- Use a stiff brush to give the black algae a really good scrub. You have to scrub really hard and continue for a long time.
- Turn of the pump.
- Use chlorine tablets or similar to treat the areas where black algae are visible. (This is not recommended to sensitive surfaces.)
- Use a suitable algaecide to treat the areas where black algae are visible. Let the algaecide work overnight. The algaecide should not be diluted; use concentrated algaecide.
- Turn on the pump.
- Brush away as much dead black algae as possible.
- Vacuum to waste.
- If the pool was heavily infested with black algae, repeat the entire process from step 1. If not, proceed to step 13.
- Check the pH-value and adjust if necessary.
- Superchlorinate the pool.
- Use algaecide to prevent future problems.
Do not let anyone swim in the pool during the anti-black algae treatment, because these chemicals are not healthy in the concentrations used to kill black algae.
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