Does Chlorine Kill Algae? The Straight Answer You Need

Do you want to know the truth about does chlorine kill algae? Discover the answer you’ve been searching for in this informative post.

Navigating the world of swimming pool maintenance can be a complex task, especially when it comes to handling microscopic invaders like algae. Ever wondered if does chlorine actually kill algae? You’re not alone!

This article is here to break it down for you. We’ll discuss how does chlorine kill algae, why it’s in your pool, and whether it can fight green algae.

What is Chlorine?

Chlorine is a chemical element with the symbol Cl and atomic number 17. It is a highly reactive, yellow-green gas commonly used in various industries, including water treatment, paper production, and different chemicals.

One of the most common uses of chlorine is as a sanitizer. Chlorine is highly effective at killing bacteria, germs, and microorganisms that can cause diseases and infections. This is why it is commonly used in swimming pools, hot tubs, and other water systems to keep them clean and free of harmful bacteria.

Chlorine is also effective at killing algae, which are simple, plant-like organisms that can grow in water systems and cause problems such as discoloration and foul odors.

However, it is essential to note that the effectiveness of chlorine in killing algae depends on several factors, including the concentration of chlorine in the water, the type of algae present, and the duration of exposure. In some cases, additional treatments may be necessary to eliminate algae from a water system.

How Does Chlorine Work?

When keeping your pool clean, chlorine is a popular choice. But how does it work? How does chlorine kill algae? Let’s find out.

Chlorine is a sanitizer that kills bacteria, germs, and other microorganisms that can make you sick. It oxidizes them, breaks down their cell walls, and destroys them.

Chlorine 2

Adding chlorine to your pool forms hypochlorous acid (HOCl) and hypochlorite ions (OCl-). These chemicals are what do the work of killing bacteria and other microorganisms.

Hypochlorous acid is the more effective of the two chemicals, but it’s also more volatile. That means it breaks down quickly, especially in sunlight. Hypochlorite ions are less effective, but they last longer.

To ensure your pool stays clean, you must maintain a certain level of free chlorine. That’s the amount of chlorine that’s available to do the work of killing bacteria and other microorganisms. Most experts recommend a free chlorine level of 1-3 parts per million (ppm).

So, does chlorine kill algae? The answer is yes, but it depends on the type of algae and how much chlorine you use. Chlorine works by disrupting the energy transport system in the algae cells, which prevents them from carrying out cell division. This eventually kills the algae.

However, some types of algae are more resistant to chlorine than others. And if you use enough chlorine or your pool water is balanced, the algae may not be eliminated.

Can Chlorine Kill Algae?

If you have a swimming pool, you are probably familiar with the problem of algae blooms. Algae can grow in your pool and make it look unappealing, and it can also be harmful to your health. That’s why it’s essential to keep your pool sanitized, and one of the most common sanitizers used is chlorine. But does chlorine kill algae?

Chlorine Filter

The short answer is yes; chlorine can kill algae. It is one of the most effective ways to eliminate algae in your pool. Chlorine works by breaking down the cell walls of algae, which causes it to die. However, the effectiveness of chlorine can depend on the type of algae you are dealing with.

Several types of algae can grow in your pool, including green algae, yellow algae, mustard algae, and black algae. Green algae are the most common pool algae and are relatively easy to eliminate with chlorine. Yellow and mustard algae are more resistant to chlorine and may require a higher concentration or longer exposure time. Black algae are the most difficult to eliminate and highly resistant to chlorine.

If you are dealing with pool algae, it’s important to identify the type of algae you have so you can choose the proper treatment method. You can do this by taking a sample of your pool water to a pool store or using a pool test kit.

pool algae 1

In addition to using chlorine to kill algae, it’s also important to maintain proper pool chemistry and filtration. This can help prevent the growth of algae in the first place.

Chlorine vs. Algaecide

When preventing algae in your swimming pool, you may wonder which is more effective: chlorine or algaecide. Both are commonly used to treat and prevent algae growth, but they work differently.

Chlorine is a powerful disinfectant that kills bacteria, viruses, and other contaminants in your pool. It works by breaking down the cell walls of these microorganisms, which causes them to die. Chlorine is also effective at killing algae, but it may not be enough to eliminate an algae problem.

Algaecide, on the other hand, is specifically designed to kill algae. It works by disrupting the cellular process of algae, which causes it to die. Algaecide is often used as a supplement to chlorine to help prevent and treat algae growth.

So, does chlorine kill algae? Yes, it does. But if you have a persistent algae problem, you may need to use an algaecide in addition to chlorine to eliminate the issue.

It’s important to note that not all algaecides are created equal. Some are more effective than others, and some are designed to target specific types of algae, such as yellow/mustard algae. Additionally, using too much algaecide can lead to the buildup of phosphates in your pool, which can encourage algae growth.

To prevent algae from taking hold in your pool, it’s essential to keep your pool clean and free of debris. Regularly brushing your pool walls and floors can help remove dead algae and prevent algae spores.

How to Use Chlorine to Kill Algae

Chlorine is a common and effective way to kill algae in your pool. Here’s how to use it:

1. Test the pH and chlorine levels in your pool. The pH should be between 7.2 and 7.8, and free chlorine levels should be between 1 and 3 parts per million (ppm). Total chlorine levels should be no higher than 5 ppm.

2. If the pH is too high, add sodium bisulfate to lower it. If it’s too low, add sodium bromide to raise it.

3. If the free chlorine levels are low, add calcium hypochlorite or trichlor to raise them. If they’re too high, add water to dilute the pool.

4. Shock your pool with a chlorine shock treatment if the algae are severe. Follow the instructions on the shock treatment package carefully. This will raise the free chlorine levels to 10 ppm or higher, killing the algae.

5. Brush the pool walls and floor with a nylon brush or wire brush to remove any remaining algae.

Brush the pool walls and floor with a nylon brush

6. Run your filtration system for at least 24 hours to remove dead algae.

7. Test the pH and chlorine levels again to ensure they’re within the recommended range.

8. Vacuum the pool to remove any remaining debris.

Vacuum the pool

Remember, it’s important to maintain proper sanitizer levels and a functioning filtration system to prevent algae growth in the first place. Regularly test your pool water and clean your pool to keep it algae-free.

Preventing Algae Growth

To prevent algae growth in your swimming pool, there are several steps you can take. Here are some tips:

1. Maintain Proper Water Chemistry

Maintaining proper water chemistry is critical to preventing algae growth. Monitor your pH levels, total alkalinity, and calcium hardness. High pH levels can cause cloudiness and scaling, while low pH levels can cause corrosion and eye irritation. Total alkalinity helps stabilize pH levels, while calcium hardness prevents water from becoming too soft or hard.

2. Use Chlorine Regularly

Chlorine is a popular sanitizer that kills germs and microorganisms in the water. It can also help prevent algae growth when used regularly. Make sure to test your chlorine levels frequently and add more when necessary.

3. Ensure Proper Filtration and Circulation

Your pool’s filter and circulation system are crucial in preventing algae growth. Ensure your filter is clean and working properly, and run your pump for at least eight hours daily to ensure proper circulation.

4. Remove Contaminants

Contaminants such as leaves, dirt, and debris can contribute to algae growth. Skim your pool regularly and use a pool vacuum to remove sediment from the bottom.

5. Consider Using Algaecide

If you’re still experiencing algae outbreaks, consider using an algaecide. Copper-based algaecides are popular, but be aware that they can stain your pool if not used properly.

Maintaining proper water chemistry, using chlorine regularly, ensuring proper filtration and circulation, removing contaminants, and considering algaecide use when necessary can help prevent algae growth in your swimming pool. And remember, does chlorine kill algae? Yes, it does – but prevention is key!

Frequently Asked Questions (FAQs)

  • How to quickly eliminate pool algae?
    • To quickly eliminate pool algae, you must shock your pool with chlorine. This process involves adding a large amount of chlorine to your pool to kill the algae. You can also use algaecide with chlorine to help eliminate the algae faster.
  • What is the natural way to kill algae?
    • If you prefer a natural way to kill algae, you can use baking soda, vinegar, or borax. These natural remedies can help lower your pool’s pH level, making it difficult for algae to survive. However, remember that these natural remedies may not be as effective as chlorine or algaecide.
  • Can vinegar be used to kill algae in a pool?
    • Yes, vinegar can be used to kill algae in a pool. However, it is not as effective as using chlorine or algaecide. Vinegar can help lower your pool’s pH level, making it difficult for algae to survive. But, it may take longer to eliminate the algae.
  • What is the required chlorine level to kill algae?
    • The required chlorine level to kill algae varies depending on the severity of the algae growth. You need to maintain a chlorine level between 3-5 ppm (parts per million) to prevent algae growth. You may need to shock your pool with a higher chlorine concentration if you have severe algae growth.
  • How long does it take for chlorine to kill algae?
    • Chlorine typically takes 24-48 hours to kill algae in a pool. However, the time it takes to eliminate the algae depends on the growth’s severity and the chlorine concentration used. You may need to repeat the process if the algae are not eliminated after the first treatment.

Overall, does chlorine kill algae? Yes, chlorine is an effective way to kill algae in a pool. However, it is essential to maintain the proper chlorine levels and use algaecide if necessary to prevent future algae growth.


Chlorine is a powerful sanitizer that kills algae, bacteria, and other microorganisms in your pool. However, it is essential to understand that not all types of algae are created equal. Green algae, yellow algae, and mustard algae are generally easy to treat with chlorine, while black algae can be more resistant and require more aggressive treatment. 

Keep in mind that while chlorine is indeed effective against algae, it should not be solely relied upon for the overall cleanliness and health of your pool. Regular filtration, pH balance checks, shock treatments, and periodic brushing and vacuuming are also necessary. It’s all about crafting a comprehensive, multi-layered approach to pool maintenance. 

Remember, prevention is always better than cure. Regular testing and adjusting of your pool’s chlorine levels can prevent the onset of an algae bloom, saving you significant time and effort in the long run.

Photo of author

About the author

Brian Anderson

The rather dry pool world out there is in need of some passion to make it shine. With the help of my son Ruben and his wife Maria our mission is to help you create the favorite spot of your house - your pool.

Related Articles...

Leave a Comment