One of the most important things you need to know about pool algae is how quickly it can take over a swimming pool if left untreated. Algae spores are microscopic organisms that thrive in warm temperatures, poor water circulation, and unbalanced pool chemicals. For pool owners in Australia, understanding the causes, types, treatment, and prevention methods is essential to keeping a clean and algae free backyard pool.
Pool Algae Types and Identification
Understanding the different types of pool algae is the first step toward effective pool maintenance.
Green algae is the most common and typically causes cloudy pool water, turning it into a green pool. Green algae is the most common type of algae in residential pools. It spreads quickly, especially in pools with poor filtration or inconsistent chlorine levels.
Yellow algae, also known as mustard algae, is often mistaken for pollen or rust. Yellow pool algae, also known as mustard algae, is often mistaken for pollen or rust. It forms in sheets, tends to grow in shady areas of the pool, and is more chlorine resistant than green algae.
Pink algae is not truly an algae but a form of bacteria. It creates slimy, reddish films and is often found in fibreglass pools or tropical climates where warm temperatures accelerate its growth.
Black algae is the most difficult to remove. Often mistaken for mould, black algae in pool environments grows into large clusters that can expand to the size of a dinner plate. Black algae appears as dark spots on pool surfaces and is difficult to remove due to its protective layer. These stubborn black algae spots are deeply rooted, thanks to their cyanobacteria structure, and can burrow into concrete pools, tile grout, or plaster finishes.
Importantly, both mustard algae and black algae are resistant to chlorine, which is why regular brushing and proper water balance are crucial. Both mustard algae and black algae are resistant to chlorine, making them more difficult to eliminate. Algae spores can enter the pool through wind, dirt, swimming costumes, pool toys, or organic matter like plant debris. Algae in your pool will multiply rapidly if conditions such as warm sunlight, inconsistent chlorine, and poor water circulation are present.
What Causes Black Algae in Pools?
Several factors contribute to black algae infestation. Black algae can take hold when spores enter through contaminated swimwear, pool equipment, or windborne dust. Once settled in areas with poor water flow, these spores begin to colonise surfaces like pool walls or floors.
Poorly maintained pools with inconsistent chlorine levels, poor filtration, or unbalanced water chemistry provide an ideal breeding ground for algae growth. Warm temperatures and low levels of sanitiser such as free chlorine allow the algae to flourish. Black algae thrives in shaded areas, particularly in crevices and porous surfaces where manual brushing is less frequent.
Is Black Algae in Pools Dangerous?
Yes, black algae can pose risks to both the pool and swimmers. Although it is not toxic on its own, it often harbours dangerous bacteria underneath its outer layer. These bacteria can cause rashes, fever, diarrhoea, and eye infections. For swimmers with open wounds or sensitive skin, the risk of infection increases.
Algae also make pool surfaces slippery, increasing the risk of slips and injuries. In some cases, airborne algae spores released in poorly maintained pools can lead to respiratory problems. Worse, algae blooms can create a breeding ground for waterborne diseases like Cryptosporidium, E. coli, and Giardia.
From a structural perspective, black algae damages pool surfaces, leading to costly resurfacing or tile replacement. This is especially true in fibreglass and concrete pools, where the algae can root into the finish.
How to Get Rid of Black Algae in Your Pool
Removing black algae requires a systematic approach. Begin by brushing affected areas using a stiff pool brush to break through the protective layer. Scrubbing the walls and floors of the pool helps dislodge algae. This step is crucial for disturbing the roots embedded in the pool surface. Focus on the pool walls, steps, tile grout, and shady areas.
Next, test your water chemistry for pH, alkalinity, and calcium hardness. Once levels are balanced, apply a heavy pool shock with liquid chlorine. Shock your pool to eliminate algae and bacteria by raising chlorine levels. Use a flocculant if early stage algae bloom is present to clump algae together for easier removal.
Apply a black algae remover or strong algaecide. For mild cases, algaecide alone may suffice. Run the pool pump continuously for at least 24 to 48 hours to circulate the pool chemicals and ensure all areas are sanitised. Afterwards, vacuum the pool to remove dead algae and debris. Skimming the surface will also help eliminate floating particles that reduce chlorine’s effectiveness. After scrubbing, you should vacuum the pool to remove dislodged debris.
Backwash your filter to remove collected algae and clean it thoroughly. Failing to do so may reintroduce spores into the clean pool water. Backwashing your filter after treatment is necessary to remove collected algae and debris.
Black Algae Removers and Treatment Options
There are several effective products for treating black algae. Copper based algaecides, chlorine boosters, and enzyme solutions are commonly used. Be sure to choose treatments compatible with your pool surface and follow the manufacturer’s directions.
Treatments may require repeat applications. Some pool owners also find success with combining algaecide and flocculant, followed by brushing and vacuuming. Flocculants are particularly useful for addressing early blooms before they become difficult to manage.
Professional pool services may use industrial strength solutions or acid washing for persistent infestations in older or poorly maintained pools.
Pool Algae Prevention Tips
Prevention is better than cure. Here are proven ways to prevent algae in your swimming pool:
- Shock your pool weekly to maintain consistent chlorine levels and kill algae before it spreads
- Run your filtration system daily to ensure proper water circulation and reduce poor water flow that encourages algae growth
- Use algaecide weekly to inhibit the growth of new spores
- Remove dead spots in the pool by improving return flow patterns and adjusting pool jet direction
- Test and balance your water chemistry frequently, especially pH, alkalinity, and calcium hardness
- Install a fibreglass pool if you are building or resurfacing, as the smooth surface resists algae attachment better than rough surfaces
- Use algaecide once every week to help control algae growth
Regularly brush pool surfaces and clean filters. Rinse all pool toys and swimming costumes before entering the pool. Clean the skimmer box weekly to avoid build up of organic matter and reduce the risk of algae infestation. Remove organic matter from the pool regularly to maintain water quality.
Other Common Types of Pool Algae
Green algae causes green pool water and slimy surfaces. It floats freely in the water and is the easiest to treat, provided that pool chemicals are used correctly.
Mustard algae or yellow algae, forms in shady areas and clings tightly to walls. It often goes unnoticed and may be mistaken for dust or sand. It grows in sheets and can resist even strong doses of chlorine.
Pink slime is a bacteria that mimics algae and typically forms in corners, behind ladders, or around pool equipment. It requires similar treatment protocols as algae due to its persistence.
Understanding the types of algae will help you choose the right treatment and prevent future blooms. Algae thrive in warm temperatures, especially in water with inconsistent chlorine levels or improper water balance.
When to Call a Professional
If your pool remains green, slimy, or develops recurring black algae patches despite multiple treatments, it may be time to contact a professional pool service. A technician can test your chemical balance, assess your pool size, evaluate filtration efficiency, and detect circulation issues that contribute to ongoing problems.
Professionals have access to industrial tools and specialised products not available in standard pool shops. They can perform deep cleaning, chemical treatments, and system upgrades to restore your pool algae free condition quickly and safely.
Final Thoughts
From green slime to black algae infestations, keeping your pool clean and safe requires vigilance and consistency. Understanding what causes black algae in pools, how to identify the different types of pool algae, and how to treat and prevent them will give you the confidence to enjoy a crystal clear swimming pool year round.
Regular maintenance, balanced water chemistry, and using the right products will ensure your pool remains clean, healthy, and inviting. Whether you tackle it yourself or call in the experts, staying proactive is the best way to protect your investment and enjoy stress free pool ownership.Things You Need to Know About Pool Algae
With over 20 years of industry experience, Adrian Mole is the founder of 1 Pool Care, a leading mobile pool service in Perth. Known for his expert knowledge and reliable service, Adrian delivers professional pool cleaning, equipment repairs, and water balancing across the metro area. Backed by SPASA accreditation, he’s committed to quality, convenience, and customer satisfaction.
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