Free delivery on orders over £50

Help! My Pool is Black

Black Algae is the least common type of Algae, but the most problematic! Unlike Green or Mustard Algae, Black Algae has strong roots and forms a layered structure with each layer protecting the layer below it, therefore surrounding itself in a protective barrier. This means it is especially resistant to Chlorine but each layer can be broken down with a bit of elbow grease to eliminate it!

Black Algae is mostly seen in Pools with a porous surface such as Concrete, Gunite or exposed aggregate. The strong roots embed in cracks in the surface and appear as black spots or blotchy patches which usually appear in areas where there is lack of water circulation. It is extremely uncommon for Black Algae to form on a liner Pool, but not unheard of.

Common prevention techniques for Algae include;

  • Maintaining a Chlorine level of 2 – 4 ppm
  • Brushing at least once a week to keep it clean
  • Run your Filter for at least 8 hours in a 24-hr period
  • Reduce the amount of Phosphates (keep below 500 ppm)
  • Keeping your Pool water below 80 degrees

To kill the Algae, you need to ‘Shock’ treat the Pool using Liquid Chlorine (Sodium Hypochlorite)

Seek advice for removal of Black Algae from Liner Pools. Do not use the method below.

What to do

Check and address the chemical levels before adding any chemicals. The chemical levels must be balanced before tackling the Algae.

Add an Algaecide directly to the affected area. This will offer another angle of attack from the Chlorine. Algaecides are specifically designed to kill and help to prevent Algae from growing so it’s a good idea to have it in the water at all times. 

Add Liquid Chlorine to the Pool. This should be added as close to the affected area as possible and at the end of the day when there is less sunlight. This means the Chlorine has longer to work before UV Rays start burning it off.

Brush the areas really hard with a stiff brush to breakdown the protective barrier the Algae has formed. This will allow the Algaecide and Chlorine to do their job.

Improve water circulation. As mentioned above, Black Algae usually turns up in areas where there is lack of water circulation so try and aim your water return jets in a way that moves the most amount of water around. If you can direct the jets to make a whirlpool effect, then you will have maximum movement.

Attack the Algae head on! Continue to regularly brush off the top protective layer of Algae and add the Chlorine as close as you can while it is exposed. You can also sprinkle some Chlorine Granules directly to the affected area and let it sit to burn off the Algae. Alternatively, you can rub a Chlorine tablet to the area after you have brushed it. Remember to wear non-porous gloves.

Rinse and repeat and you will eventually get rid of it! Water balance and scrubbing is the best thing to do and how fast it will go depends on how bad the Algae is but you will get there.