How To Deal With Black Algae In Concrete Pools

Finding slimy algae in your swimming pool is never a pleasant experience, but keeping your swimming pool free of black algae is especially important. This insidious and highly resistant form of algae can rapidly contaminate the most well-maintained swimming pool, and concrete swimming pools are particularly vulnerable to developing black algal blooms.

What Is Black Algae?

Technically speaking, black algae is not algae at all. It is actually a type of bacteria known as cyanobacteria, which shares a close resemblance to 'true' algae species.

Like true algae, cyanobacteria contains chlorophyll, which it uses to photosynthesise sunlight and convert it into energy. This chlorophyll gives the cyanobacteria its blue-green hue. Black algae cyanobacteria also contain chlorophyll but are so dark that they appear black under most lighting conditions.

Black algae usually finds its way into swimming pool water when a swimmer enters the pool with black algae spores attached to their body. Contamination is particularly likely if a bather swims in a river, lake or lagoon before entering the pool, as natural freshwater sources usually contain many varieties of algae. Black algae spores can also be carried on the wind and into your pool water, although this is less likely.

Fortunately, black algae is rarely harmful to humans, although black algae blooms have been known to harbour dangerous bacteria such as E. coli. However, black algae blooms growing on your pool's walls and bottom can be very unsightly, and the dark pigments contained within their bodies can leave permanent stains on your pristine pool surfaces.

Why Are Concrete Pools Vulnerable To Black Algae?

Black algae usually only grow on porous surfaces, so you are unlikely to see black algae growth in a vinyl or fibreglass pool unless the pool is very old. Unfortunately, concrete's porous, textured surface is an ideal breeding ground for black algae, and small patches of black algae can rapidly spread across the walls and bottom of almost any concrete pool.

The corners and edges of concrete pools are especially likely to harbour black algae blooms, as these locations are sheltered from underwater currents and allow the algae to grow and breed. Removing black algae from these tight crevices can be very challenging.

How To Remove Black Algae From Concrete Pools

If you spot black algae growing in your concrete pool, you must remove it as quickly and thoroughly as possible, before it has a chance to leave permanent stains on your pool surfaces. Unfortunately, black algae removal can be a laborious, multi-step process.

The first step is to check the pH levels of your pool water and adjust them using high-quality pH chemicals if necessary. The pH of pool water should be kept at around 7.4 to deter algae growth. Black algae are more likely to thrive in pools with high pH levels.

From there, you will need to add algaecidal chemicals to your pool regularly, and scrub at the black algae blooms with a wire algae brush on a daily basis until the algae have been completely eradicated. This can be time-consuming, to say the least, and you may find it difficult to find consumer-grade algaecides that are powerful enough to destroy black algae.

With this in mind, your best bet is to call in a professional swimming pool cleaning service if your pool has become infested with black algae. These services have access to commercial-grade algaecides and water sterilisation chemicals, will save you a lot of back-breaking scrubbing, and possess the knowledge and experience to quickly find and destroy every trace of black algae in your pool