Algae in the pool is often a recurring and frustrating problem for pool owners.
It can appear suddenly, especially if it is not properly maintained.
The appearance of algae is a clear indicator that something is out of balance in the pool water. To understand why it happens, there are several factors that directly affect its proliferation.
Main factors promoting algae in pools
One of the main factors is chemical imbalance in the water. When chlorine, pH or alkalinity levels are not in their optimum ranges, the water becomes more prone to algae. In our professional experience, the first, first, first thing is to do a water test.
Without knowing what is going on in the water, we cannot know for sure why algae are appearing.
The most common reason is the presence of nutrients such as phosphorus or nitrogen, which serve as food for algae. We have also observed that, although the water may appear crystal clear, it is possible that there are nutrients on the walls of the water, which can lead to the appearance of algae.
Another aspect is the lack of circulation in the water.
If the water velocity is low or the filtration system is not working properly, algae can settle in more easily.
In my experience, if the water is circulated quickly in certain areas, pockets of algae can form due to the high concentration of nutrients passing through those areas.
Nutrients and phosphorus in the water
Excess phosphorus in the water is a major contributor to algal blooms. This nutrient can enter the system through various sources, such as make-up water, organic waste or even cleaning products.
On one occasion, after performing a water test, I discovered an excessive amount of phosphorus. This led me to investigate the source of this nutrient, as the biological filter or the plants should be able to absorb these nutrients. If the amount of phosphorus is too high, the filtration system can be overwhelmed, allowing algae to appear on the pool walls.
Types of algae in swimming pools and how to identify them
There are several types of algae that can appear in a pool, each with its own particular characteristics. Identifying them correctly is the key to applying the right treatment and eliminating the problem at its root.
Green algae
Green algae are the most common and tend to grow in areas where there is poor water circulation. These algae are easy to identify as they dye the water a cloudy green colour. In my experience, this type of algae can appear quickly if chlorine levels are not adjusted.
Wall moss is also a form of green algae and usually appears in pools where nutrients such as phosphorus are out of balance.
Yellow algae
Although less common than green algae, yellow algae are persistent and more difficult to remove. Yellow algae tends to grow in the shadier areas of the pool and can resist normal chlorine. If you decide to brush the walls, be careful, as removing them without eliminating the source of the problem will only cause them to reappear.
Black algae
Black algae are the most difficult to eradicate. They form colonies in cracks and rough surfaces, and once they are established, it is difficult to remove them completely. Black algae require more aggressive treatments and close monitoring of water chemistry.
Effective methods to remove algae in swimming pools
Removing algae from a pool is not simply a matter of brushing the walls or adding more chlorine. It is necessary to understand the causes that have led to their appearance and to apply an appropriate treatment.
Water testing: the essential first step
As mentioned above, a water analysis is the first thing you must do.
Without this step, any measures you take may not be effective. On one occasion, after testing the phosphorus and chlorine levels in my pool, we discovered that the problem was coming from the quality of the make-up water.
This allowed us to adjust the treatment accordingly and control the algae growth.
Use of chemicals vs. natural methods
Once the problem has been identified, several methods can be used to eliminate algae.
Chemicals, such as chlorine and algaecides, are the most commonly used and effective in the short term.
However, in a natural pool, unlike a traditional chlorine pool, we do not recommend scraping off the algae biofilm without first removing the nutrients that are causing it, as this can make the situation worse.
On the other hand, in natural pools, it is advisable to use more sustainable methods, such as increasing the capacity of the biological filter or introducing plants that absorb the nutrients.
This may be slower, but in the long term it will prevent algae recurrence.
How to prevent algae in swimming pools
Once you have removed the algae, the next step is to make sure it does not return.
Prevention is key and requires constant maintenance, on the other hand it is normal for algae to appear occasionally after the summer when nutrients have increased due to the use of the pool and it is time to overwinter.
Control of nutrients in the water
Keeping the levels of nutrients such as phosphorus and nitrogen under control is essential to prevent algae growth.
If your make-up water contains too many nutrients, you may not be able to prevent some algae growth, but you can reduce it with a proper filtration system.
In this case, increasing the capacity of the biological filter and improving control of high phosphorus water inputs was key to keeping my pool free of algae.
Improved circulation and filtration
The pool’s circulation and filtration system plays a crucial role in algae prevention.
Make sure that the water is moving properly and that the filter is in perfect condition.
If the circulation is poor, even the best maintained pools can develop areas of moss. One solution we implemented was to install a more powerful circulation pump, which significantly improved the cleanliness of the water.
As you can see in biopools algae can also appear and the resolution is not as fast as in a conventional chlorine pool as we do not use chemical treatments, but you are also assured of water with less nutrients (chlorinated).
