Causes of Green Algae: Understanding What Turns Your Pool Water Green

No one wants to swim in a green pool—it looks like a slimy, smelly ditch. Swimming in such dirty water is not only uncomfortable but can also spread germs and cause health issues. The main culprit behind this phenomenon is the growth of green algae. If you find yourself facing these green intruders in your pool, don't worry; 85% of pool owners have been there. By understanding them and taking appropriate measures, you can lead your pool out of crisis.

On warm, sunny days, green algae can double in quantity every 24 hours. Once they find their way into your pool and get the right conditions to thrive, these microorganisms can quickly become a nuisance. Knowing about these organisms is crucial for addressing the issue.

Green algae are the most common and easiest type of algae to remove from pools. Depending on the severity, the color of green algae can range from teal green, which is easier to remove, to dark green and the most severe, dark blackish green. Its sources are widespread, not only found in natural bodies of water but also entering your pool through precipitation.

Compared to other types of algae like black algae, green algae are relatively easy to spot in pools. In warm, sunny environments, they form a thin film on the water surface, accompanied by a slimy texture.

Temperature and Sunlight: Green algae thrive in temperatures above 70°F. During summer, when temperatures rise and pools are not cooled to a normal range, green algae can reproduce rapidly. Direct sunlight also provides nutrients for photosynthesis, accelerating their growth. 

Low Chlorine Levels: Free chlorine in water is crucial for disinfection and killing germs. When temperatures rise, chlorine decomposes excessively or is not supplemented adequately, leading to low chlorine levels that fail to effectively kill bacteria, algae, and other contaminants, providing an opportunity for green algae to proliferate. 

pH Imbalance: pH is an important measure of the acidity or alkalinity of pool water, ranging from 0 to 14, with higher values indicating higher alkalinity and lower values indicating higher acidity. The normal pH range for pools is 7.2 to 7.6, ensuring a good swimming experience and effective action of disinfectants. If the pH is too high or too low, the effectiveness of chlorine, the most important component of disinfectants, is affected, failing to kill algae and creating a perfect environment for green algae to flourish. 

 Insufficient Circulation: Algae prefer stagnant water, similar to the green ditches often seen in parks. When there is plenty of sunlight and insufficient water circulation, algae can grow wildly. Therefore, running the pool pump for 6-8 hours in winter and 10-12 hours in summer can effectively prevent the proliferation of green algae. 

Filter Issues: When the filter is clogged with debris or faces blockage, water circulation is disrupted, preventing the effective removal of green algae particles. Regular inspection and cleaning or backwashing of the filter are necessary to ensure its proper working efficiency.

To prevent green algae from entering your pool, it's essential to understand its sources and take proactive measures to keep it at bay. The best approach to dealing with algae is prevention. Here are some useful steps to keep algae out of your swimming pool:

1. Balance Chemical Levels:

Algae thrive in environments with imbalanced pH and free chlorine levels. Regularly check your pool's chemical levels weekly to ensure the pH is between 7.2 and 7.6, and the free chlorine level is between 2.0-4.0 ppm. There are many solutions available on the market for testing these chemical values.
Test strips are the simplest and quickest way to check these chemical levels, although they may not be as accurate as other products.
Take a test strip from its packaging, holding the white end without touching the colored part to avoid damaging the strip and causing inaccurate results. Always replace the cap after use to prevent the strip from deteriorating.
Immerse the strip in a well-circulated area of the pool, ensuring the colored part is fully submerged. After removing it from the water, wait 30 seconds for the strip to change color. Then, compare the color on the strip to the chart to determine the levels of pH, total alkalinity, total chlorine, and free chlorine in your water.

2. Ensure Proper Filtration:

Algae prefer stagnant water, so poorly circulated water can be a breeding ground for algae. Run your pool pump for several hours each day, and if you notice algae at the bottom of the pool, run it continuously for 24 hours. To prevent debris that attracts algae from accumulating, clean your filtration system thoroughly before using the pool pump. If you have a sand filter or DE filter, backwash them regularly.

To backwash a filter, turn the multi-port valve handle or slide the push-pull valve, then restart the pump and run it for 2-3 minutes until the water runs clear. After that, close the pump, move the valve back to the filter position, and reopen the filter.

3. Brush the Pool:

To remove stubborn green algae particles, physical removal is the most effective method. Manually scrub the pool walls, using a metal wire or hard pool brush for concrete or plaster pools. Thoroughly clean all surfaces of the pool, including steps, walls, corners, and ladders, where algae tend to grow.

4. Use a Pool Cover:

To prevent algae particles from being blown or washed into your pool, consider installing an automatic safety cover. It can also keep your pool free of debris particles, which can help attract and spread algae.

By following these steps, you can effectively prevent algae from entering and thriving in your pool, ensuring a clean and enjoyable swimming environment.

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