Does Shock Kill Algae?

Swimming is a signature summer hobby for many, and it can be a year-round activity for those who own a pool. But what if your pool starts to look greenish and algae infest your watery oasis? You may be wondering, can I shock the algae away?

Shocking or rapidly increasing the chlorine levels in a pool can kill algae. Unfortunately, it may take more than one treatment to do so. Completely eradicating algae with shock treatments may require you to administer up to three shock doses over a 36-hour period.  

The rest of this article will explain a few topics related to this question in great detail, including how much shock is needed to kill algae, how long it takes, how to shock your pool, and the after-effects of doing so.  

Can Shock Kill Algae?

Cloudy water, green slime, and odors steaming from your pool?  It’s likely because algae is growing in your pool water.  Not to worry, you can shock it to eliminate it.

Shock can kill algae if the dosage is strong enough and the proper steps are followed.  Running your pool filter, especially throughout the shock treatment, is crucial to fully eradicating algae.  

Continue reading to learn more about shock treatments on algae growth. 

How Much Shock Is Needed To Kill Algae?

Pool shock is a means of quickly jolting your pool back to the proper and safe chlorine levels. For example, shocking should be done if your pool is growing algae or when the free chlorine levels (FC) measure zero. Other times to shock your pool are after a storm or eliminating pool waste. But how much should you use?

How much shock you need depends on the size of your pool and the type and severity of the algae. If the water in your pool appears very discolored and greenish, or you can see algae clinging to its walls or floor, you may need to use shock up to three times to kill the bacteria and algae growth.  

However, if your pool is only slightly discolored or there’s only a slight smell, you may not need as much shock to kill the algae.

Another factor to consider is the size of your pool. If you have a larger body of water, you may need to increase the amount of shock.  

Three types of algae could be in your pool, so it’s crucial to figure out which type you have when trying to determine the correct shock dosage. The three types are as follows: 

  • Green algae: This is the most common type of algae. You can typically tell if you have green algae because it’s usually green in color, floats, and has a slimy texture.  
  • Yellow algae: These algae are much rarer than green algae. Yellow algae are sandy or brownish and are particularly troublesome because they are chlorine resistant. However, yellow algae can still be killed by shock treatment, but the shock treatment should be more aggressive than it would be for eradicating green algae.  
  • Black algae: This is the most aggressive type. Black algae produce their food so they can grow more rapidly than the other types of algae. Unfortunately, this feature also makes it troublesome to eliminate. 

All of these types can be killed with shock, but, again, you should adjust the amount of shock that you use depending on the type and severity of the algae.  

To avoid algae build-up, proper filtration and sanitation systems are crucial. 

To learn more, check out this article from DIY Pool Supply.   

How Long Does It Take Shock To Kill Algae?

Shock treatment is effective at eliminating algae and bacteria in your pool. However, it’s also a major waiting game.  

It can take up to 36 hours for shock treatment to kill algae. Therefore, after applying shock to your pool, you should wait at least six hours before testing the PH and chlorination levels in your pool.  

After shocking your pool, you should test the water again to ensure that the PH and chlorine levels are proper.  

Even though it can take several days following a shock treatment before your pool is safe to use again, it’s essential to complete the treatment. 

Algae in your pool are dangerous for your health and safety. Algae can release toxins in a body of water – pool water or otherwise. According to this article, algae that grew following a heavy storm in Toledo, Ohio, in the spring of 2014 shut down the entire city’s water supply. When professionals tested the water, they found many nasty toxins, making it unsafe to use. 

Ensure that you complete your shock treatment when you have algae growing in your pool to prevent health hazards for anyone who uses your pool.   

How To Shock Your Pool

According to the same article mentioned above, the US economy loses $2 billion a year from algae water damages. So if your pool is growing algae, it’s essential to take care of the problem immediately to avoid expensive water treatments and devalued properties.

The goal when shocking your pool is to raise the chlorine levels by ten times the combined chlorine level.  There are multiple types of chlorines used in pools.  The three most common are: chlorine gas, sodium hypochlorite, and calcium hypochlorite. These chlorine levels will need to be increased ten fold to combat algae growth.     

Also, make sure to shock your pool at dusk or night. According to PLOS One, the sun and heat can help algae survive. Additionally, the sun burns off chlorine. So, for your shock treatment to be effective, you must perform the treatment after the sun goes down. This can also make waiting easier because the chemicals can work while you sleep.  

Here is how you can shock your pool in ten easy steps: 

  1. First, vacuum the pool to get rid of waste and sediment collecting at the bottom.
  2. Second, brush the walls and sides of your pool to remove algae from the structure.
  3. Next, test the water’s PH and chlorine levels with a pool test kit.
  4. Fourth, calculate how much shock is needed.
  5. This step is optional, but you can add granular pool shock to help eliminate the algae. 
  6. Next, ensure that your pool pump is working. 
  7. After checking on your pump, pour the shock mixture into the water around the edges of your pool.  
  8. Then, let the pool pump run for about six hours or more to filter out the algae. You should run the filter until the water is no longer cloudy or discolored.  
  9. Finally, test the water again, but wait at least six hours before doing so.   
  10. Wait to swim until chlorine levels are at 1 – 3 ppm. 

Make sure that while you’re shocking your pool, you wear protective gear. Rubber gloves and goggles are a must-have!

For a more detailed guide on how to shock your pool, check out this video from Swim University:


Shocking” is simply adding high levels of chlorine to a pool to bolt it into a cleaner state. Pool shock gets rid of algae and bacteria, and professionals recommend doing it regularly.  

Preventative measures are just as necessary, if not more so than shocking your pool, though. Proper filtration and sanitation tactics are vital for the cleanliness and integrity of your pool. 

Jed Arnold

Jed spent every year from the ages of 15 - 22 as a Lifeguard (Red Cross) and ages of 17 - 22 as a Certified Pool Operator (CPO). Between working for over a dozen facilities and owning a pool, he carries over a decade of pool experience.

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