Black algae are aquatic photosynthetic bacteria called cyanobacteria. They are single-celled, but grow in large colonies. They contain chlorophyll, but they also contain compounds called phycobilins, which mask the green colour of chlorophyll. There are two types of phycobilins: phycocyanin, a blue pigment, which gives the cyanobacteria their name, and phycoerythrin, a red pigment, which exists in red or pink algae (often found around sinks or drains). Cyanobacteria are very important organisms that assist in the growth of many types of plants. They are one of very few organisms that can convert inert atmospheric nitrogen into a form that plants can use such as ammonia (NH3) or nitrate (NO−3).
These bacteria can grow protected from the surrounding environment. This is due to the formation of a ‘sticky layer’ on the outside of the cell. The process of photosynthesis, carried out by the bacteria, depletes carbon dioxide (CO2) in the surrounding water. The decrease in carbon dioxide concentration causes the precipitation of calcium carbonate (CaCO3) in that area. As a result, calcium carbonate, along with any other sediment that may precipitate, becomes trapped within the sticky layer. The bacteria will then grow through and over the sediment continuing to photosynthesize and develop.
This process will occur over and over again forming more layers and making the black algae more difficult to treat. Brushing is extremely important when treating black algae as the protective layer must be broken in order for the sanitizer or algaecide to come in contact with the cyanobacteria.
Nutrients and algae growth
Nutrients, such as carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorous (P), sulfur (S) and even water (H2O) and sunlight are essential for the metabolic processes of many different types of plant life. However, as there are more than 7,000 species of green algae, the optimum nutrient requirement varies widely between algae species. Thus, it is impossible to predict the minimum nutrient level required for a specific type of algae that may exist in a particular pool. This is an important point to understand when it comes to the prevention and treatment of algae in swimming pools.
Within the pool/spa industry, phosphorous has been singled out to receive undue attention as it relates to its effect on algae. While phosphorous plays an important role in photosynthesis and respiration, research has shown most species of algae have the ability to store phosphorous within their cells, an evolutionary phenomenon known as ‘luxury phosphorous uptake.’ This means that algae have the ability to stockpile phosphorous when in nutrient-rich environments to allow for continued growth when exposed to nutrient-deficient environments. This is a defence mechanism algae have to help them survive. Therefore, efforts designed to starve algae by removing phosphates as a method of prevention are insufficient to replace the proven effectiveness of a government registered algaecide.
The addition of nutrients to a lake or pond may increase algae growth and therefore disrupt the balance of the ecosystem. For this reason, there are often limits for discharge of nutrient-containing water into lakes and streams to avoid upsetting this balance. The pool environment is completely different; therefore the same limits do not apply. A pool environment includes filtration as well as the use of sanitizers and algaecides, which are toxic not only to algae, but to other aquatic life as well. In addition, industry standards such as American National Standards Institute (ANSI)/Association of Pool & Spa Professionals (APSP)-11, Standard for water quality in public pools and spas and ANSI/APSP/International Code Council (ICC)-5 2011, American national standard for residential inground swimming pools have no restrictions on the amount of phosphate (or nitrate) in pool water.
The growth of algae will be effected by the presence of sanitizer and/or algaecide. For example, hypochlorous acid (HOCl) will enter the cell wall of bacteria or algae and disrupt metabolic activity, whereby stopping its growth even in nutrient-rich surroundings. It is important to choose products for algae treatment or prevention that have been properly registered by the Canadian Pest Management Regulatory Agency (PMRA). Registration is a rigorous process that requires the submission of supporting data. Compounds that currently carry PMRA, or Environmental Protection Agency (EPA) registration for algae treatment include hypochlorous acid, hypobromous acid (HOBrO), ammonium chloride quats, polyquats, copper (Cu) and silver (Ag).
The use of a maintenance algaecide contributes to improved water quality and helps prevent problems before they begin. In the event of an algae bloom, immediate treatment is the key to having the pool up and going again as soon as possible.