There are many thousands of species of algae in the world, and these organisms produce more than half of the world’s oxygen. They are an important part of life on earth, but we don’t want to invite them to a weekend pool party! Pools are constantly being bombarded by algae from various sources, so controlling it can be a challenge. However, keeping algae from growing in a pool is a vital part of proper pool care maintenance. Let’s take a closer look at ways to prevent algae growth and what to do if an algae outbreak occurs.
So, what do we know about algae? The first question that always comes up is where does algae come from? A pool can go from crystal clear to swampy green overnight in some situations, and it’s often difficult to figure out how it got there. Algae is constantly being introduced to the pool from a variety of sources. Algae spores of varying species are found in natural water sources, plants, soil and trees. Rain, wind, swimmers and birds are just a few more of the sources that introduce algae to pools. One bird can introduce more than 100 types of algae to the swimming pool environment. The short answer is that algae are introduced from everywhere.
If algae prevention measures are not present once algae spores are introduced into the pool, they will immediately start to grow and reproduce. Unchecked, one algae cell eventually can become more than 1 million algae cells and cause algae to bloom in the pool. A key to keeping pools clean and clear is to prevent algae growth and reproduction from occurring. Getting rid of an algae outbreak is much more difficult than preventing an outbreak from happening in the first place.
In the pool industry, algae are typically classified into three categories: Green, Yellow (or Mustard), and Black Algae. There are general characteristics associated with each category of algae. Green algae tend to be the easiest type of algae to get, but also the easiest to get rid of. Pools can turn green quickly but can also be cleaned up quickly in most instances. In many cases, an EPA-registered chlorine-based shock treatment, paired with good circulation and filtration, can take care of the issue.
Yellow algae, also known as Mustard algae, is a yellow color and can usually be found on the bottom of the pool. If brushed up, yellow algae will “fluff” up, but usually settle again in the same area of the pool. This can make it difficult to vacuum up to remove it.
Black algae, which is actually not algae at all, is a very different growth on the pool surface. Black algae, which is actually cyanobacteria and not algae at all, clings to the pool surface, rooting into the plaster and becoming very difficult to brush up and remove. Hard brushing and direct application of chlorine or algaecide to the black algae (cyanobacteria) growth is usually the best way to remove it. Be sure to spot test the area first before direct application treatments.
Most pool care experts have a plan for each type of algae, a recipe that seems to work the best to remove it. Recently, however, scientists and chemists have conducted targeted research to determine if there was a better way to prevent and kill the algae commonly found in swimming pools. This research entailed an extensive review of publications on algae research combined with collecting algae from various pool environments, as well as test pools in research facilities. Once collected, these naturally occurring algae samples were identified and classified, then used in a wide variety of experiments to determine the most effective way to control and kill each unique sample.
As discussed, algae are classified into three general groups in the pool industry. In reality, there are actually 13 major groups of algae. These groups are classified by a variety of characteristics, including what kind of chloroplasts are found in the algae cell, what kind of reserves they feed on, what makes up the outer membrane of the algae cell, whether they move about via flagella and many other features. These are the characteristics that help determine the best way to prevent and treat algae, as opposed to just using the color or location of the algae as the main point of classification for pools.
Let’s start with the most common type of algae in pools: green algae. The most common type of green algae in pools is called Chlorella sorokiniana.Chlorella sorokiniana is a vibrant green color and makes up the majority of green algae that was identified in the study’s pool samples. Chlorellasorokiniana is controllable with chlorine, and most of the algaecides common to pool care programs. This type of algae was expected to be present in the pool samples collected. In “green” algae samples, however, a different type of algae was also identified. This algae is called Scendesmus acutus, a completely different species of green algae than what we typically reference in the industry. When looking at a pool, however, the only classification visible is that the algae is green. There is no visible difference between the two species of algae unless placed under a microscope. Under the microscope, Chlorella sorokiniana is round and independent, while Scendesmus acutus, is oval shaped and creates long chains of algae cells in groups.
As the research progressed on how to effectively kill green algae, it showed that while chlorella is easily killed by chlorine, quat- or polyquat-based algaecides or copper-based algaecides, Scendesmus acutus does not respond as well to low residuals of copper. Have you ever used a copper algaecide and expected it to clear the pool quickly, only to find that it doesn’t seem to be effective on the algae growth? Depending on the quantity of algae in the pool, repeated applications may not seem to work any better in these situations. In these cases, the green algae in the pool could be Scendesmus acutus, instead of the more commonly encountered chlorella. How, you might ask, can that be identified poolside? Unfortunately, it can’t.
The scope of this research also encompassed an in-depth look at mustard algae. The most common type of mustard algae in a swimming pool is Eustigmatos vischeri. Eustigmatos vischeri is yellow in color and exhibits the common characteristics you’ve come to expect of mustard algae—it settles to bottom, brushes up and is difficult to control. The algae species is round and appears to be covered by a hard outer shell. This shell can make some species of eustigmatos more resistant to chlorine, which would would require higher levels of chlorine in order to control it. The need for higher levels of chlorine can lead to problems holding a chlorine residual in the pool, and could ultimately lead to a chlorine demand. However, because they are ingested into the algae cell instead of breaching the outer cell wall, copper-based algaecides are very effective against mustard algae.
In the process of classifying mustard algae, real-world pool samples yielded another species that looked like mustard algae in the pool but was another species entirely. On the surface, it looked like Eustigmatos vischeri, but it was actually Nitzschia communis. Nitzschia communis is a diatom that presents as mustard algae but is a completely different organism. It has flagella and can move around under its own power in the water. Nitzschia communis actually feed on silica to enhance reserves needed for survival. In a pool environment, a sand filter or other dirt and debris from the surrounding environment provide an unending source of silica for these diatoms, allowing them to grow and reproduce. In many cases, pools that have mustard algae have a high reoccurrence of an outbreak after the algae is initially controlled. This is often due to the lack of chemically cleaning the filter itself after an algae treatment. If Nitzschia communis is growing in a pool, not cleaning the filter will allow it to continue to grow and reproduce even after treatment. Eventually the entire pool will be impacted again, and the cycle continues.
Chemically cleaning the filter after any algae outbreak is an important part of the treatment process. Additionally, the presence of dirt (which contains silica) in areas of poor circulation at the bottom of the pool can lead to an environment where Nitzschia communis is more easily able to grow and reproduce.
The final classification of algae in pools is “black algae.” As mentioned, black algae are not actually algae at all, but rather cyanobacteria. Cyanobacteria is filamentous, which means it will root down into the pool surface in order to anchor and grow. These filaments make it difficult to release “black algae,” aka cyanobacteria, from the surface of the pool to treat it. In addition to filamentous roots, cyanobacterial also has a hard shell that covers the layers of growth, making brushing an important part of the treatment. Common consensus says that cyanobacteria is most likely to grow in areas of the pool surface that are rough or damaged, allowing the algae to take root. The research showed that cyanobacteria was most likely to grow in areas of the pool with poor circulation. Cyanobacteria is often found in corners of the pool, as well as on the steps—both areas where circulation is poor and the environment is right for cyanobacteria to root and grow. This is one of the many reasons why brushing a pool is an important part of weekly maintenance. Pools should be brushed weekly, regardless of if there is a visible issue or not.
This research confirmed that there are varying types of algae that naturally occur in swimming pools. It’s impossible to identify exactly what type of algae is growing just by looking at the color of the algae material in the water. In this study, there was a mixture of different types of algae present in most samples collected. This makes it difficult for pros working poolside to identify the right type of algae treatment necessary to effectively kill and prevent algae outbreaks.
While there’s no one silver bullet to keep in your toolbox, this research should encourage you to consider a variety of approaches to treat the different types of algae you may encounter in the field. Chlorine is a great algaecide and is effective against many types of algae found in pools. Maintaining normal sanitizer residuals is usually enough to prevent algae outbreaks. Allowing that level to drop below the recommended range, however, even for a few hours, can allow some fast-growing algae to begin spreading. Once algae have begun to grow, it may take higher levels of your sanitizer to control them. It is much easier and more economical in the long run to always maintain that normal sanitizer level in the water.
Chlorine’s main job, however, is to kill bacteria in the water. The sanitizer in the pool is the only chemical that kills bacteria. Utilizing chlorine to kill algae might be effective in most cases, but it uses up a lot of chlorine in the process, leaving less behind to kill bacteria. Other algaecides, such as quats, polyquats or copper-based algaecides don’t have any other job to do other than kill algae, leaving chlorine available to kill bacteria.
The research focused on finding an effective way to kill algae, independent of the sanitizer and without adverse effects such as foaming or staining. General characteristics of algaecides tell us that chlorine can be effective in many cases, but quats and polyquats are easier to help manage water chemistry. Quats and polyquats are positively charged molecules that are attracted to the negatively charged cell wall of the algae. Like a magnet, the algaecide and algae cell are pulled together, then the quat or polyquat will tear open the algae cell wall, causing the algae cell to die.
Copper algaecides work differently. Copper algaecides are ingested into the algae cell, shutting down the internal processes and enzymatic reactions that keep the cell alive. Copper algaecides are very effective against many species of algae and are often among the fastest acting algaecide treatment options.
Because most algae blooms found in pool water are a mixed bag of algae species, it is impossible to determine which algaecide will be the most effective for each pool. This is where the value of newer advanced technology such as multi-functional algaecide is evident. Researchers posed the question “How do we formulate an algaecide that is effective against ALL types of algae?” After extensive research, scientists determined that a blend of highly chelated copper, along with a polyquat-based algaecide and some additional proprietary ingredients created a synergistic effect that was highly effective against all types of algae, even showing results in eight hours. This revolutionary new blend allows efficient and effective algae treatment, without relying solely on the use of chlorine for algae control.
Maintaining a pristine swimming pool that’s free of algae is essential for the health and safety of swimmers. Proper pool maintenance, including a constant sanitizer residual, weekly shocking and the addition of a preventive algaecide are key elements to keeping pools clean, clear and ready for swimming. Ideally, no pool would ever experience an algae outbreak. However, the use of a multifunctional algaecide can ensure the fastest and most effective solution to the problem. Ultimately, customers want pools that are great to look at, safe to swim in, and provide a comfortable and relaxing experience. Being up to date on the latest algae treatment and prevention methods is a key element to providing a pristine pool for swimmers to enjoy.
About the Authors
Alicia Stephens is the director of training and education for Biolab Inc. In her 23 years with Biolab, Alicia has focused primarily on education, training and development, as well as technical support and new product research and integration.
John Weber is a senior formulation chemist with BioLab, where he is primarily responsible for new product development, supporting existing products and evaluating new technologies. John has been in the pool and spa industry for more than 26 years. John has worked with and/or been a member of the Recreational Water Quality Committee of PHTA for many years and teaches numerous courses on water quality at trade shows annually.