Understanding algae

October 1, 2011

By Karen Rigsby and Zach Hansen

In order to prevent or treat algae successfully, one must understand the different types and characteristics of the algae they are treating.

Algae are microscopic aquatic plant-like organisms. They do not have the same structure as higher plants such as roots, stems and leaves. However, they are like any other plant in that they require the same type of nutrients to grow and utilize sunlight to carry out photosynthesis. In swimming pools, algae can be quite a nuisance; however, they are actually the most important photosynthesizing organisms on earth. They capture more of the sun’s energy and produce more oxygen (a by-product of photosynthesis) than all other plants combined. In addition, many species of animals depend on algae as a food source.

Algae size can vary greatly and they can grow in a number of different habitats. It can endure a wide range of temperatures and has been found growing everywhere from hot springs to deep within polar ice. Microscopic algae, called phytoplankton, are typically found in lakes and oceans. The largest forms of algae are seaweeds, which can grow up to 91.4 m (300 ft) and stretch from the bottom of the ocean to the surface of the water. Although most algae grow in water, they can also grow on soil, trees, under or inside porous rocks and even on some animals.

Types of algae in swimming pools

When it comes to swimming pools, algae can be a common problem that becomes a pool owner’s nightmare. In order to prevent or treat algae successfully, one must understand the different types and characteristics of the algae they are treating.

Green algae

Green algae can be free-floating or surface-clinging and can be found in lakes, rivers, ponds and swimming pools.

Green algae are the most common with more than 7,000 different species in existence. Approximately 10 per cent of these are marine species (found in the ocean) with the remainder being found in lakes, rivers, ponds and swimming pools.

Green algae are named for the chlorophyll (the molecule that captures light energy to carry out photosynthesis) in the cell, which gives them their green colour. It can be free-floating or surface clinging and can be found in all types of pools. They are typically the easiest to treat; however, some species may be more difficult to manage than others.

Mustard algae

Mustard algae have been described as ‘adapted green algae.’ Mustard algae also contain chlorophyll, but the green colour is masked by the presence of beta-carotene. Carotenoids (such as beta-carotene) are found in many photosynthetic organisms. These compounds are responsible for colour (like the orange colour of carrots) which is why mustard algae are yellow rather than green.

Carotenoids are anti-oxidants (or reducing agents). They protect against damage caused by oxidation. Mustard algae can use these compounds as a defence mechanism to help them survive in a chlorinated environment. As carotenoids protect against oxidation, chlorine (Cl) (as an oxidizer) may have little effect on algae once this defence mechanism has been activated within the cells.

Black algae

1930`s era Public open air Lido swimming pool[2]
Black algae are single-celled, but grow in large colonies. Brushing the pool’s floor and walls is extremely important when treating this type of algae.

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 (NO3).

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.

How algaecides work

Quaternary ammonium compounds (quats) are positively charged and are therefore attracted to the negative charge on the cell wall of the algae. The quat’s wetting agent properties as well as this charge attraction allow it to enter the cell wall, which causes it to break. The structure of the quat makes a difference when it comes to the effectiveness of the product. Quaternary ammonium compounds have a ‘chain’ of carbons on the molecule and these carbon chains can vary in length. Through research and testing, it has been determined that biocidal activity peaks at a carbon chain length of 14.

Polymeric quat compounds work in a similar manner to ammonium chloride quats. However, because they are much larger molecules, they usually work a little slower than ammonium chloride quats.

Copper is effective at killing algae because it disrupts enzymatic activity within the cell.  If the enzymes do not function properly, the organism cannot survive.

Preventing algae growth

The physical aspect involved in pool care should be kept in mind. Proper circulation and filtration, as well as routine cleaning and vacuuming of the pool surface are very important.

Ultimately, proper maintenance is the key to keeping algae growth in check. The most important consideration is the presence of sanitizer, or even better—sanitizer and algaecide. Establish a maintenance system that includes maintaining appropriate sanitizer levels, routine oxidation and application of a preventative algaecide. Remember, algae treatments will be much less effective if the pool is unable to maintain a sanitizer residual.

The physical aspect involved in pool care should also be kept in mind. Proper circulation and filtration, as well as routine cleaning and vacuuming of the pool surface are very important—particularly brushing (as mentioned previously). Once algae are exposed, the products applied for sanitization and algae prevention are able to do their job, allowing them to work more effectively.

Using products that are PMRA or EPA registered as algaecides and always following product application directions will help ensure successful treatment and a more enjoyable pool experience for the homeowner.


Rigsby_HeadshotKaren Rigsby is the leader of technical services for BioLab, a Chemtura Company. She has been involved with the recreational side of water treatment since 2001, focusing on education, problem resolution and new product development. She began her career in the water treatment industry at BioLab as an analytical chemist in the research and development group. Prior to recreational water, Rigsby was employed by the Georgia Bureau of Investigation as a forensic chemist. Rigsby received her bachelor of science in chemistry from Georgia Tech and is a member of the Association of Pool & Spa Professionals (APSP) Recreational Water Quality Committee and a National Swimming Pool Foundation (NSPF) certified instructor.


Hansen_HeadshotZach Hansen is a new product specialist for BioLab, where he started his career working in automated controller and feeder equipment development. Over the last four years he has focused on new product commercialization and development for the company. Hansen received his bachelor of science degree in chemical engineering from Auburn University in 2004. He can be reached via e-mail at zach.hansen@chemtura.com[4].

  1. [Image]: http://poolspamarketing.com/wp-content/uploads/2011/10/bigstock_Green_Algae_3530572_edited-1.jpg
  2. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/06/dreamstime_m_1357818.jpg
  3. [Image]: http://www.poolspas.ca/wp-content/uploads/2015/06/dreamstime_l_15782874.jpg
  4. zach.hansen@chemtura.com: mailto:zach.hansen@chemtura.com

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