What Causes Algae in Your Pool? (Pool Algae Species Overview)

Combating algae plays an important role in pool maintenance and crystal clear water.

But how do algae develop in the pool, and which types of algae are most common?

This article will explain how pool algae grow and what promotes algae growth in pool water. You will also find helpful tips on fighting algae at the end.

The formation and growth of algae in the pool

Algae are small, plant-like creatures that mainly live in water and carry out photosynthesis.

The algae are an essential part of nature and live in peaceful coexistence with other plants and living things. These even serve as a food source for animals and produce vital oxygen.

Nevertheless, we do not want any algae in our pool water because they can make the pool cloudy.

But how do algae develop in the pool, and can this be prevented?

The algae can reproduce themselves sexually and asexually. Asexual reproduction occurs through simple cell division – this is also referred to as a clone because the subsequent generation is genetically identical to the parent.

Mainly when the water balance is disturbed, there is an intense build-up of algae in the pool, and the water becomes dirty.

This disturbance of the water balance always occurs when at least one of the following points occurs:

  • An increased supply of nutrients allows the algae to grow. This nutrient includes leaves, insects, grease, and other contaminants in the pool water.
  • Warm pool water and a lot of direct sunlight lead to optimal living conditions for the algae in the pool.

The truth is: You will never get rid all the algae out of the pool. The only option here is to inhibit the algae bloom through proper water treatment.

If there is a problem with algae in the pool, a corresponding pool cleaning is necessary to eliminate this. However, to do this, you first have to identify the type of algae.

Different types of algae in the pool water

I have already described in detail in my blog article how to remove the different types of algae from pool water.

But which algae are in the pool, and what do algae look like in the swimming pool?

In the following chapters, you will find a complete overview and description of the different types of algae that occur in swimming pools.

Green algae in the pool

The green algae (Chlorophyta) is probably the most common algae that every pool owner will become acquainted with.

You can recognize the green algae as a light green coating, which mostly appears on the walls and in the pool’s corners.

Despite good pool values, especially when the air is humid, the pool water can be full of this stuff overnight after a storm.

The algae growth often happens when the filter run times of the pool pump are less than 6 to 8 hours per day.

Brown pool algae

The brown algae (Phaeophyta) are rich in shape and can appear in the pool with tiny filaments or form large structures.

This type carries out a generation change and can cover a large pool quickly. Source.

But it is also possible that you only have dead algae in the pool. When algae die off due to chlorine or other disinfectants, they often turn brown.

But one thing is sure: This type of algae should be removed from the pool as quickly as possible because the digestion produces gases.

Yellow algae (mustard algae)

Mustard algae (Chrysophyta) are rare and more of a common problem in the United States.

Suppose you have discovered yellow algae in the pool water. In that case, it may have been brought into the pool by birds or contaminated swimwear.

Have you been to a quarry pond with the same swimwear – without washing them beforehand – and then went into the pool? This may be why you have yellow algae in the pool. Or you are simply mistaking it for sand in the swimming pool.

Fortunately, yellow algae are relatively easy to get rid of, like green algae.

In the article, I explain how to remove mustard algae in your pool. Just follow the link.

Black Algae (Blue Algae) in the swimming pool

Black algae (Cyanophyta) are often found in pools alongside green algae.

But the black algae (also known as blue algae) does not belong to the algae and is a bacterium. These bacteria are often introduced into the swimming pool by birds or humans from nearby water.

As a rule, this type of algae only affects concrete pools. This is because cracked joints in the concrete pool are popular standing places for black algae.

Black algae rarely appear in the PVC pool due to the surface but can also arise in this pool.

Due to the complex structure of the black alga, it is challenging to clean. In addition, this type of algae is dangerous for human and animal health.

Don’t worry: You can read how to remove black algae in your pool and prevent new growth in my article.

Pink algae (pink slime)

The pink algae in your pool is not a type of algae.

Like black algae, this bacterium occurs predominantly in PVC pools and can be very slimy – hence the name pink slime.

The bacterium only gets its typical red color when it comes into contact with pool chemicals. Before that, the pink algae is transparent.

You can find more information about the pink algae and how to remove it from your pool in my blog article.

White algae in the pool

I researched white algae in the pool for a long time and found that this problem often occurs on hot days above 30 ° C – But I could not find white algae.

The assumption was based on improper use of the flocculant or the poplar tree seeds.

The assumption that the poplar tree was the cause could be refuted due to the season. A small test using pH-Minus and pH-Plus can also deny the flocculant as a cause of white pool algae.

If you see white algae in your pool and it looks like fluffy cotton, it is most likely bacteria in your pool.

White algae in your pool are also known as bacterial lawns and are often a sign of poor pool water hygiene.

What promotes algae growth in the swimming pool?

It is essential to know what is promoting the growth of algae in your pool to take targeted action against them.

Algae usually develop when the filter run times are too short or when the disinfectant does not work.

As long as the filter pump runs too short and green deposits form on the bottom, the solution is to increase the circulation time of the filter system.

If the disinfectant has a weak effect, I recommend testing the water regularly and treating it accordingly with the products I have described.

But even with good water values, it is not uncommon for algae to settle in your pool. The reason may be the pool technology, but weather-dependent influences also play a role.

Do not waste too much time looking for why algae are present in your pool.

First, orient yourself in my blog to the emergency measures against algae. After that, you must do your pool maintenance routinely and check with a visual inspection whether algae form again.

What helps against algae in the pool?

I have explained how algae are formed in your pool, which types can occur in the pool water, and I have already briefly indicated what promotes algae growth.

With this information, you already suspect what helps against algae in your pool.

Nevertheless, I want to list specific measures here that can help you inhibit algae growth in your pool.

  • Increase water circulation: Make sure that your pool pump runs for 6 to 8 hours a day. On cold days, 4 hours are enough.
  • Optimize the pH-Level: Make sure that the pool water has a pH of 7.2 to 7.6. Everything below or above has to be optimized.
  • Reducing light: You can prevent direct sunlight in the pool by covering the pool with a tarp when it is not in use.
  • Eliminate nutrients in the pool: Phosphate, nitrate, iron, and other colloidal contaminants serve as food for algae and must be removed with water filtration.
  • Use disinfectants: Use chlorine or another disinfectant for water treatment in the pool to kill the algae.
  • Use flocculant: Microalgae can be filtered out more easily with the sand filter system by using a flocculant.
  • Use algaecide: The algae bloom can be inhibited with the help of an algaecide agent (algae agent) – I recommend foam-free agents.

If you still have a problem with algae, I recommend my instructions against algae in your pool, which I have linked to you.

Then it would help if you read through my instructions for pool maintenance so that no more algae develop.

Do you have any further questions about algae in your pool?

Contact me at @contactswimfool on Twitter, Facebook, YouTube, or Pinterest.

I am happy to help you personally.

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Hi. I'm Max Berg. I've been in the pool industry since 2015 and have always felt drawn to water. I'm the author behind swimfool.com, where I share my years of experience in pool maintenance and give helpful tips on keeping a swimming pool or hot tub clean. My tips reduce the costs of water treatment and protect the environment.

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