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How Do I Get Rid of Green Algae In My Pool?

How Do I Treat A Pool Filled With Green Algae? 

Green algae in a swimming pool is an all-too-common and frustrating issue for many pool operators. It can turn your crystal-clear water into a murky green mess, making your pool unsightly and unsafe to swim in. While there are various methods to combat this problem, it may come as a surprise that using chlorine is the most effective and recommended approach over algicides. This article will guide you through the process of treating green algae in your swimming pool using chlorine.

What is Algae?

Green algae are microscopic plants that thrive in warm, sunny conditions, especially when the pool's chlorine levels are low. They can quickly multiply, turning the water green and forming slimy layers on pool surfaces. Algae not only makes the pool unattractive but can also harbor harmful bacteria.


Why Choose Chlorine Over Algicides For Pool Algae?

Algicides can be helpful in preventing algae growth, but they are not as effective at killing established algae. They can also introduce high metal and mineral content into your water, which can cause major headaches down the line. Chlorine, on the other hand, is a powerful oxidizer that not only kills algae but also destroys bacteria and other pathogens. Here are some of the main reasons to choose chlorine:

  1. Effectiveness: Chlorine is more effective at eliminating algae and preventing its return.
  2. Cost-Effective: Chlorine is generally cheaper than specialized algicides.
  3. Multi-Purpose: Chlorine not only kills algae but also keeps the pool water sanitized and safe for swimming.


Step-by-Step Guide to Treating Green Algae with Chlorine

Step 1: Test the Water

Before you begin, test the pool water to determine the current chlorine levels, pH, and alkalinity. Ideally, the pH should be between 7.4 and 7.6, the alkalinity should be between 80-120ppm, and the chlorine level should be between 3-4 ppm. Adjust the pH if necessary, as high or low pH can reduce the effectiveness of chlorine.

Step 2: Brush the Pool

Use a pool brush to scrub the walls, floors, and any other surfaces where algae are visible. This helps to break up the algae and makes it easier for the chlorine to do its job of eliminating the green algae from the swimming pool. 

Step 3: Hyperchlorinate the Pool

Hyperchlorinating the pool involves adding a large dose of chlorine to kill the algae. Follow these steps:

  • First, make sure the pool is closed and no swimmers are present in the water
  • Calculate the amount of chlorine needed. Generally, you'll need to raise the chlorine level to 10-15ppm to fully eliminate the algae
  • Use a high-quality chlorine product and follow the manufacturer's instructions for application. It's best to do this in the evening to avoid chlorine degradation from sunlight.
  • Pour the chlorine evenly around the pool, especially in areas where algae are most concentrated

Step 4: Run the Pool Pump

As always, keep the pump running to circulate the water and ensure the chlorine is evenly distributed. This helps to filter out dead algae and other debris.

Step 5: Vacuum the Pool

After a few hours, vacuum the pool to remove the dead algae and other debris that have settled at the bottom. If your pool has a lot of debris, you may need to backwash the filter frequently to maintain proper filtration.

Step 6: Test and Balance the Water

Test the water again to check the chlorine levels. If the chlorine level is still high, drop it down to the normal range (3-4 ppm) using sodium thiosulfate before allowing swimmers back into the pool. Also, ensure the pH and alkalinity levels are balanced.

Step 7: Maintain Regular Pool Care

To prevent the return of algae, maintain proper pool chemistry by regularly testing the water and keeping the chlorine levels within the recommended range. It is especially crucial to make sure you're keeping your chlorine levels in ideal range (3.75-4.5ppm). Also be sure to brush the pool surfaces at least 3 times a week, and shock the pool as needed, especially after heavy use or rainfall.


Preventive Measures

  • Maintain Chlorine Levels: Keeping chlorine levels consistently at 3-4ppm will prevent algae from re-appearing
  • Consistent Cleaning: Brush and vacuum the pool regularly to remove debris that can harbor algae.
  • Proper Circulation: Ensure the pool pump and filter are running efficiently to keep the water circulating and clean.



Treating green algae in your swimming pool using chlorine is a straightforward and effective method. By following the steps outlined above, you can restore your pool to its crystal clear, blue state and ensure it remains safe and enjoyable for swimming. For more information on how to professionally operate your pool, consider getting your CPO Certification if you haven't already. You can get your certification through Pool Training Academy's award-winning training staff and learn how to keep you pool in perfect shape! For more information about Certified Pool Operator certification click here

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