Pool Algae: Types, Causes, and Treatments

A pristine swimming pool is a luxurious addition to any property — so long as it is algae-free. 

The appearance of pool algae can quickly turn an aquatic haven into a murky, unappealing sight. While algae growth can certainly be unsightly in a swimming pool, the more pertinent issue at hand is the hygienic concerns leading to the growth and accumulation of algae. 

In this article, we discuss the ins and outs of pool algae and how to remove it. From the different types of algae that can grow in a pool to the causes behind algae growth and the necessary treatments, we cover everything you need to know about pool algae and how to deal with it. 

Keep reading to learn how to restore and maintain your pool’s crystal-clear allure! 

Types of Pool Algae 

Algae is a type of non-flowering aquatic plant that is a single-celled organism that can grow in almost all types of bodies of water. This plant relies on photosynthesis to thrive and can grow at incredibly rapid rates with access to plentiful sources of nutrients, sunlight, and carbon dioxide. 

However, not all types of algae are the same. According to the U.S. Department of Energy: “The term ‘algae’ actually encompasses an incredibly large and genetically diverse group of organisms. Genome sequencing has found algae in four different kingdoms: Plantae, Chromista, Protista, and Bacteria. Algae can be unicellular or as large as a tree like the giant sea kelp.” 

The diverse nature of algae has resulted in some confusion surrounding algae in pools, especially when it comes to the underlying cause of algae growth and how to treat it. 

With this in mind, let’s take a look at the three primary types of algae found in swimming pools: 

Green Algae 

Green algae is the most common type of algae found in swimming pools and is likely what you picture when you hear the term “algae.” Biologically, green algae contain chlorophylls that give this type of algae its iconic and highly recognizable green pigmentation. 

When green algae grow in pools, it can appear as a green tint or layer floating at the pool’s surface. Green algae can also contribute to an overall cloudy appearance in pool water. 

In terms of how green algae survives in a swimming pool, it often has to do with the presence of phosphates and nitrates introduced into the water by-products on the skin and hair of swimmers, as well as chemicals and other substances entering into the pool from rain run-off. 

Green algae can thrive in both still and moving water. It tends to proliferate under certain conditions, such as when the pool water has an imbalance of nutrients and inadequate disinfection. When conditions are favorable — such as during the summertime when warm temperatures and constant sunlight are a regular occurrence — green algae can multiply rapidly on the surface of pool water. 

Preventing the growth of green algae requires regular maintenance of a pool’s water chemistry, with a special focus on chlorine levels and pH balance. 

Chlorine is commonly used as a disinfectant in pools because it effectively kills algae and other microorganisms. Regularly testing and adjusting pool water chemistry, along with proper filtration and circulation, help prevent the growth of green algae and keep the water’s surface clear. 

Yellow Algae (Mustard Algae) 

Yellow algae — also called mustard algae — is a subclass of green algae that has grown to be resistant to swimming pool chemicals. Whereas green algae primarily grows and spreads on the surface of pool water, yellow algae is more pervasive and can grow in patches on pool walls, steps, and shaded areas. 

In general, yellow algae occurs less commonly than green algae. Despite this fact, yellow algae can still be a real pain due to its resistance to normal green algae treatments. 

The appearance of yellow algae is typically a mustard yellow-brown that forms in patches that can be mistaken for dirt, debris, or sand. This type of algae tends to have a more slimy texture compared to green algae and clings to surfaces that are in shaded areas of the pool for the majority of the day. 

Yellow algae achieves its resistance to chlorine and other chemicals thanks to the development of compounds that defend the plant organism from chemical processes. 

Even when the chlorine levels in the pool are within the acceptable range for sanitation, this type of algae can persist if it has already begun to form and grow within the pool water. The chemical-resistant nature of yellow algae can be traced back to the development of the aforementioned protective layer. 

To effectively treat yellow or mustard algae, a multi-pronged approach is often necessary and should include vigorous brushing, shock treatments, and algaecides. 

Ideally, you should aim to inhibit the growth of yellow algae altogether by addressing green algae growth as soon as possible and focusing on boosting prevention through regular maintenance and treatments. 

Black Algae 

Black algae is generally considered the most tenacious form of pool algae, making it the most difficult to treat and eliminate after it forms. While black algae have the same chlorophylls that give green algae its green hue, it is also comprised of other compounds that darken the plant to an almost-black color. 

In a pool, black algae can have a slimy texture and tend to form in any cracks and crevices in the pool floor and walls. This type of algae can become deeply rooted in pool surfaces and is extremely resistant to standard pool chemical treatments, making black algae a formidable adversary. 

The appearance of black algae often looks like slimy patches or lines that can be mistaken as stained or darkened parts of the pool itself. These spots can vary in size and often develop in areas where the pool surface is rough, such as plaster or concrete. 

Due to black algae permeating the tiniest pores of a pool, it is extremely resistant to chlorine. 

The unique characteristics and resistances of black algae make it vital to take a more intense approach to treatment and removal. This can include the typical treatments for algae — like chlorine, algaecides, and shocking — as well as more forceful treatments that involve mechanical equipment for brushing, cleaning, and removing stubborn algae patches. 

Given the difficulty of eradicating black algae, seeking professional help or advice from pool maintenance experts may be beneficial, especially if the infestation is severe. Proper prevention and diligent maintenance are key to keeping black algae at bay and maintaining a clear and inviting pool. 

What Causes Pool Algae? 

The underlying cause of pool algae ultimately comes down to a lack of proper water maintenance. 

Issues with pool algae can be rooted in a variety of insufficient maintenance practices, including poor water circulation, unstable chlorine levels, poor filtration, and unbalanced chemicals. Collectively, this lack of maintenance can create an environment conducive to algae growth in swimming pools. 

Since swimming pools are mainly comprised of still water, disinfection is vital for keeping the pool water clean. When water is allowed to sit in a pool without adequate cleansing and upkeep, it can lead to the creation of nutrient-rich pockets that offer algae the ideal place to grow and thrive. Plus, as algae grow, the problem can only worsen as more algae support the proliferation of algae spores. 

To prevent algae growth, it is essential to address these factors through regular maintenance, proper water circulation, consistent monitoring of water chemistry, and optimization of a pool's filtration system. 

Understanding the root causes of pool algae growth is essential to preventing its occurrence and identifying the early signs of algae growth within your pool. 

Let’s take a look at the four main causes behind pool algae: 

Poor Water Circulation 

Inadequate water circulation creates stagnant areas where algae can flourish. 

When pool water is insufficiently circulated, the pool chemicals added to the water cannot reach all areas of the pool and end up leaving pockets of space imbalanced and lacking the proper disinfection. 

Over time, these pockets become the perfect breeding ground for green algae, enabling the plant to establish colonies that grow and spread the longer the issue goes unaddressed. 

Algae require nutrients, sunlight, and carbon dioxide for photosynthesis and growth. Stagnant water prevents these nutrients from being evenly distributed throughout the pool, creating pockets of excess nutrients that promote algae proliferation. Effective water circulation helps disperse these nutrients and prevents the settling of algae spores, reducing the likelihood of algae taking hold and growing. 

Unstable Chlorine Levels 

Chlorine is a powerful disinfectant that helps control algae growth. 

Insufficient chlorine levels allow algae to multiply rapidly. Conversely, excessively high chlorine levels can lead to chlorine-resistant strains of algae. 

Though chlorine is a crucial component of pool water maintenance that acts as a disinfectant, it needs to be handled with care and expertise. If left unmonitored and poorly managed, your pool’s chlorine level can hinder algae prevention rather than help inhibit the plant’s growth. 

If chlorine levels in the pool are too low, there might not be enough active disinfectant to inhibit algae growth effectively. This allows algae spores to multiply and develop into visible algae colonies.

Conversely, excessively high chlorine levels can cause chlorine "lock," a situation where the high chlorine concentration becomes ineffective at killing algae due to chemical imbalances. Maintaining stable and appropriate chlorine levels is essential for preventing algae growth. 

To keep your swimming pool in great condition and algae-free, your chlorine levels should be kept between 1.0 to 4.0 parts per million (ppm). This requires you to either measure these levels and apply the necessary chlorine yourself or enlist the help of a professional pool maintenance team. 

Here’s an overview of the chlorine measurement and application process for swimming pools: 

• Get a Test Kit: Purchase a reliable pool water test kit to measure your pool’s chlorine levels. There are various types available, including test strips and liquid kits. Test kits typically measure various parameters including chlorine, pH, alkalinity, and more. 

• Perform the Test: To perform the test, you must first collect a water sample in a clean container. Make sure the container is free from contaminants before collecting the water, then follow the instructions on your chosen test kit to measure the chlorine level. This usually involves dipping a test strip into the water or adding reagents to a sample and observing the color change. 

• Read the Results: The test kit will provide you with a reading of the chlorine level in your pool water. Ideal free chlorine levels typically range between 1.0 to 4.0 parts per million (ppm) for residential pools. If you are responsible for monitoring and maintaining a commercial pool, then it may be best to opt for a professional testing procedure. 

• Choose the Chlorine Source: There are various forms of chlorine you can use, including liquid chlorine, chlorine tablets, granular chlorine, and salt chlorine generators. Choose the form that best suits your preferences and pool type. Each type comes with its own benefits, so make sure to do your research beforehand and consult with a professional pool maintenance team. 

• Calculate the Amount: Refer to the product label on your pool water test kit for dosage instructions based on your pool's size and current chlorine levels. Follow these instructions carefully and exactly to avoid over-chlorination. If you do add too much chlorine, the best next step is to get in touch with pool professionals to resolve the issue. • Prepare and Add the Chlorine: Depending on the type of chlorine you're using, you may need to prepare it first. Once your chlorine is ready, add it to the pool water in the specified amount. For liquid chlorine, you can pour it directly into the pool. Tablets require a chlorinator or floater, while granular chlorine needs to be dissolved before adding it to the water. 

• Circulate & Re-Test the Water: Turn on your pool's circulation system, such as the pump and filter, to help distribute the chlorine evenly throughout the pool. Wait for a few hours or even overnight, then retest the chlorine levels. The goal is to achieve the appropriate chlorine level within the recommended range. 

Poor Filtration 

A malfunctioning or improperly maintained pool filter can fail to remove debris and microorganisms from the water. This creates a breeding ground for algae to thrive in, as pockets of nutrients form. 

The pool's filtration system plays a vital role in removing all types of contaminants from the water. If the filter is not functioning properly or is inadequately maintained, it fails to trap and remove particles that can serve as nutrients for algae. As a result, the pool water becomes laden with organic matter and other substances that can fuel algae growth. Additionally, poor filtration leads to uneven water distribution, creating areas where algae spores can settle and develop. 

Regular maintenance and cleaning of the pool filter are essential to prevent algae growth. 

Unbalanced Chemicals 

Maintaining proper water chemistry is paramount to preventing algae growth. Along with checking your pool’s chlorine levels, you also need to monitor the water’s pH, alkalinity, and calcium. Imbalanced pH, alkalinity, and calcium hardness levels can create an environment conducive to algae proliferation. 

For example, low pH levels can lead to corrosive water that damages pool surfaces, potentially providing a substrate for algae attachment. High pH levels, on the other hand, reduce the effectiveness of chlorine. 

Similarly, imbalanced alkalinity and calcium hardness can affect water stability and the performance of other chemicals. When chemicals are not properly balanced, algae can take advantage of the resulting conditions to establish and flourish. 

Here are the ideal levels for each of these chemicals to aim for: 

• pH Balance: The pH level in your pool should be kept between 7.2 to 7.8. When your pool’s pH balance falls below this level, the water can become acidic and cause skin and eye irritation. When the pH balance rises above this level, it becomes alkaline and can lead to a cloudy appearance, scale formation, and algae growth. 

• Alkalinity: When determining whether your pool’s total alkalinity is within a normal range, the alkalinity measurement should fall between 80 to 120 ppm. The total alkalinity of your pool water indicates the ability of the water to resist changes in pH. 

• Calcium: Calcium hardness can help prevent pool water from scaling or becoming corrosive. The ideal calcium hardness level to aim for can vary depending on the material a pool is made from. In general, your pool should fall between 200 to 400 ppm when measuring calcium hardness. 

Final Thoughts: How to Get Rid of Pool Algae in 4 Steps 

Addressing a pool algae problem requires a systematic approach. Whether you plan on handling your pool water maintenance all on your own or hiring a professional team to assist you, it is crucial to have a clear idea of how to best measure, monitor, and maintain your pool’s water. 

Here are four essential steps to effectively eliminate algae and restore your pool's clarity: 

1. Ensure Pool Pump and Filtration are Working Properly: Begin by checking the functionality of your pool pump and filtration system. Ensure that the pump is circulating water adequately and that the filter is clean and capable of removing debris and contaminants. Improved circulation prevents algae from settling and thriving.

2. Check and Balance Pool Chemicals and Chlorine: Regularly test and adjust pool water chemistry. Maintain appropriate chlorine levels within the recommended range. Shocking the pool with a chlorine-based shock treatment can help eliminate existing algae and restore proper chlorine levels. Additionally, make sure all other chemicals are kept in the appropriate ranges. 

3. Brush and/or Vaccum Your Pool Surfaces: Brushing the pool's walls, floors, and steps regularly helps dislodge algae and prevent it from clinging to surfaces. Follow up with thorough vacuuming to remove loosened debris and algae particles from the water. If you do not have the proper equipment for this task, get in touch with your local pool maintenance team. 

4. Consider a Pool Shock Treatment: If the algae infestation in your pool is severe, a pool shock treatment may be necessary. Shocking involves adding a concentrated dose of chlorine or non-chlorine shock treatment to the water. This process eliminates algae, destroys chloramines and oxidizes organic matter to bring your pool water back to a hygienic state. 

Maintaining a clear and inviting pool requires consistent care and attention. 

Understanding the types of algae that can invade your pool, recognizing their underlying causes, and implementing effective treatments are essential steps in preserving your pool's beauty and ensuring the health and safety of swimmers. 

By promptly addressing poor water circulation, unstable chlorine levels, poor filtration, and unbalanced chemicals, you can prevent algae growth from taking hold. Regular maintenance will help you eliminate existing algae and prevent their return. 

Remember, a well-maintained pool not only enhances your property's aesthetics but also provides a safe and enjoyable space for relaxation and recreation. With proper knowledge and diligent care, you can keep your pool algae-free and ready for countless hours of aquatic enjoyment.

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