Algae are microscopic single-cell plants that can enter the water from the atmosphere by the actions of wind and rain. There are over 30,000 different varieties of algae

The three main categories are: -

Green Algae

- usually free-floating although they sometimes colonise surfaces

The green algae are the fastest growing algae and are responsible for most 24-hour algae blooms

When pool water becomes turbid (cloudy) with algae it makes the pool dangerous to use, as it is difficult to see the bottom of the pool

As the water turns green the surfaces of the pool develop a slippery feel.  The water becomes hazy, pH will shoot up and chlorine levels will drop sharply

A bloom of green algae can turn a clear, clean pool into a green swamp overnight

The pH rises as algae consume the carbon dioxide (CO2 helps to keep the pH down), and the pool surfaces will be coated with a slippery Bio-film

Once algae become visible you’re in trouble.  Algae take in carbon dioxide and give off oxygen like most other plants

Most bacteria found in swimming pools take in oxygen and give off carbon dioxide

Each grows by consuming the by-products of the other, and thus the proliferation of both organisms accelerates

For this reason we use a chemical program that assures both bacterial and algae control

Mustard (Yellow) Algae

often appears on the shady side of the pool as a yellow powdery deposit.  Once established, yellow algae are Chlorine resistant and can survive in the presence of 3-5 ppm of free chlorine.  Superchlorination will kill mustard algae but the dead cells must be scrubbed from surfaces

Black (Blue-Green) Algae

evident by the formation of 1 to 3cm sized black (or dark blue-green) spots on the pool surfaces, especially on the grout lines or plaster.  Black algae form a layered structure where the first layer (which superchlorination may kill) protects under-layers from further destruction

Black algae are similar to the algae that are found on bathroom shower tiles and in silicone seams near the bath. This form of algae is very slow growing but very hardy; it is extremely Chlorine resistant

Black algae can be controlled by the use of Copper Sulphate or a Copper Ioniser

Prevention of algae

A successful program of regular pool maintenance prevents algae from growing. This is achieved by monitoring and controlling pH and residual free chlorine in the water

Application of a general Algaecide or Algaestat is also recommended.  Use Copper Sulphate at a rate of 3 grams per cubic m3. This chemical should not be applied more than 2 times per season to avoid overdosing, which can cause blue staining of the plaster or grout, green hair and blue nails

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Note: - Please contact our recommended Pool Professionals for supply and installation of all pool-related services: - 

Andalusia and the Costa del Sol - Pool Safety SpainPool Safety Spain

Nerja area - This email address is being protected from spambots. You need JavaScript enabled to view it.

Each of the above offers years of experience, free unbiased advice and excellent, Professional service.

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Ken Walker - MyPoolGuru©