Graphic by Nick Orabovic

Algae are a familiar plague of even the most diligent service techs. Changes in water chemistry and content can transform a blue pool to green in short order. Therefore, it’s important to understand what facilitates algae growth and how to appropriately treat it.

Algae are photosynthetic, meaning they contain chlorophyll and utilize sunlight and carbon dioxide (CO2) to produce glucose (for energy to grow) and oxygen (O2). Algae also need a number of nutrients in order to grow. These include nitrogen, oxygen,carbon, hydrogen, phosphorous and sulfur in addition to water and sunlight.

However, much attention has been focused around a single nutrient needed for algae growth: phosphorous. It is an essential nutrient for both plant and animal life, but techs should understand the limitations of relying on phosphorous control as a means to inhibit algae growth.

Phosphate defined

The compound referred to as “phosphate” is actually orthophosphate. It is simply a phosphorous atom surrounded by four oxygen atoms, PO4-3. It can exist as it is written (an ionic species dissolved in solution) or it can be attached to another molecule such as a protein. Phosphate comes from a variety of different sources. These include fertilizer, industrial discharge, swimmer waste, detergents and chemicals used to treat corrosion in drinking water — just to name a few.

Phosphate and algae growth

Phosphorous is, in fact, highly significant in the metabolic processes of many different types of plant life. It plays an important role in photosynthesis and respiration. However, the optimum phosphorous requirement varies widely among different types of plants.

Because there are more than 7,000 species of green algae, it is difficult to predict the minimum phosphorous level required for a specific type of algae that may exist in a pool. Some algae can thrive at extremely low levels of orthophosphate.

Algae have the ability to store phosphorous within their cells, which is known as “luxury phosphorous uptake.” This means algae can continue to grow even in a phosphorous-deficient environment. Without the presence of orthophosphate, many species of algae can convert other phosphorous-containing compounds into a usable form because of enzymes that exist at the cell surface (also known as phosphomonoesterases, or phosphatases).

There are claims that indicate using an orthophosphate remover will stop or at least inhibit algae growth in pool water. It is important to note that these products are effective at removing orthophosphate and therefore may reduce cloudy water or provide a lower TDS (total dissolved solids) level. However, they are not currently EPA- registered as algae killers (algaecides) or algae inhibitors (algaestats).

Preventing algae growth

Using products that are EPA-registered to kill and/or inhibit the growth of algae is the best option. When used appropriately, sanitizers such as hypochlorous or hypobromous acid, polyquats, quaternary ammonium compounds, and copper-based treatments are very successful in controlling algae, regardless of the orthophosphate level.

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.

But don’t forget the physical aspect involved in pool care. Proper circulation and filtration as well as routine brushing and vacuuming of the pool surface are very important. Some algae have a protective outer coating, and brushing will help break through that coating, allowing products to work more effectively.

By using products that are EPA-registered as algaecides and always following product application guidelines, you can help ensure successful treatment and a more enjoyable pool experience for the homeowner.