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Tips and tricks for identifying and treating tough algae

By Terry Arko

Some pool algae are easy to treat and remove; however, other types can be quite challenging to deal with.

As the weather warms up and the swim season starts, pool water quality begins to suffer and algae often start to grow. Some algae are easy to treat and remove; however, other types can be quite challenging to deal with. The three main types are: green, black, and yellow/mustard algae. Green algae is relatively easy to eradicate, but yellow/mustard and black algae are difficult to kill and, as a result, can make the job of a pool service professional difficult.

Green algae

The growth and spread of this algae is usually due to a lack of sanitizer and or circulation in the pool. When it is present, this algae can typically be identified by the slight cloudiness of the pool water. As it continues to grow and thrive, the water quality gets worse and, in extreme cases, it eventually deteriorates to the point where the pool steps and floor become difficult to see.

Green algae should be dealt with quickly to prevent these water clarity problems, as cloudy pool water can make it difficult to see someone who may be having trouble in the water and, thus, increase the risk of drowning.

Green algae spores are common and are typically found when chlorine levels are not maintained during especially warm, sunny periods. This algae can also be introduced as a result of cross contamination when toys or swimsuits that have been used in a river or lake are then used in the pool. Technicians using brushes and poles to clean algae, but neglect to clean them before servicing the next pool, could, in fact, cause outbreaks in the others they service. That said, green algae is by far the easiest to prevent and kill. High doses of chlorine usually eradicate it quickly; the process can also be accelerated with the addition of a good algaecide, which will also make the customer happier much faster.

Once the water has been treated to kill the algae, the pump and filter have the burden of clearing the water. The filtration system must continually run to trap the dead algae and clear the water. A water clarifier can also be used to help expedite this process. When the pool’s water is properly balanced and maintained (using chemicals and sanitizers) it is fairly rare for green algae to grow.

Black algae

This algae will generally appear as black dots on pool plaster, usually in the pitted area of the pool where the plaster has been etched or where calcium deposits have developed. These areas act as small foxholes where water does not circulate well, making it an easy area for black algae to grow and thrive.

Black algae is a problem that is almost exclusive to gunite pools. It is tough to treat because it burrows into the plaster and forms a protective layer, making standard chemical treatments ineffective. As this algae needs a place to grab onto, it becomes an even bigger problem in plaster pools where the surface has deteriorated. Cracks and rough areas around light fixtures, ladder rails, or broken tiles are prime habitats for black algae. It also tends to be more prevalent in rural, dry agricultural regions, as it can be introduced into the pool via debris in the air.

This algae should be treated as soon as it appears, as the bigger the head of the algae spot the deeper it burrows into the plaster and the harder it is to kill. There are several ways to treat it, including scrubbing the affected area(s) with a stainless steel brush for an extended period of time to remove its protective coating. Brushing should be repeated daily until the algae is eradicated from the pool. In severe cases, the spread of the algae may be controlled; however, it may not be eliminated entirely.

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