Black Algae In Saltwater Pool: Why & How to Remove?

Swimming in a saltwater pool on a hot summer day is more relaxing than anything else. But black algae is the culprit that may deprive you of this relaxation. If you swim in the water that contains algae, you will get sick. 

But removing the black algae is not like catching the leaves or dirt. It’s challenging and requires a lot of elbow grease to get rid of the virus from your pool. 

Fortunately, this guide includes 6 effective ways to remove the algae from the pool. Therefore, we also discussed what causes black algae in the Saltwater pool. So, continue to read to discover how to kill the virus to make your pool swimmable and healthy.

Black Algae In Saltwater Pool

What is Black Algae?

Black Algae, you see in your saltwater pool, frankly are not black. If you take a sample from your pool and squeeze it on white paper, you can see a greenish tint. 

True algae are single-celled organisms that contain chlorophyll like other algae. They are usually green. Now, you may ask- why do black algae look black?

Well, black algae are not algae; it’s a bacteria indeed. It’s basically cyanobacteria which also contains chlorophyll. At the same, cyanobacteria also hold other water-soluble pigments. When both blue-green and water-soluble dyes get combined, they appear black. 

Generally, true algae have nutritive value, but black algae grown in your pool are not equivalent to the true algae. And it is toxic and harmful. 

What Causes Black Algae To Grow In Your Saltwater Pool?

Black algae are like a virus. Once it grows in your pool, it can spore and spread around your saltwater pool to infect the water. Dirty water is the primary reason behind growing algae. 

Maintaining chemical balance will not prevent the black algae from growing if the filtration system doesn’t work. The virus (black algae) can propagate when the filter or skimmer stops circulating your pool water. 

You know this- when the pooling filtration system malfunctions, the water turns cloudy. And it’s the right time for the growth of black algae. 

Indeed, hot temperature, unbalanced water, and improper filtration can be developing algae in the pool. 

Nonetheless, if you have gone to sea recently, algae may ride to your pool in your swimsuit. 

Is Black Algae Harmful?

The short answer is- Yes. 

But swimming in the saltwater pool that contains black algae will not bring any damage to you or your health. In other words, algae won’t make you sick alone. 

Now, you may throw a question to us with confusion- then, why did we say it is harmful? 

Ok, let us clarify it. Black algae may contain harbor organisms or attract deadly bacteria like E.coly. And this harmful bacteria can make the swimmers sick. 

If you or your children drink the water accidentally, you may experience nausea. That’s why we say black algae is harmful. So, we suggest you keep yourself away from the pool water until you treat the algae. 

How to Remove Black Algae in Saltwater Pool?

From above, you learned about black algae, what causes it to grow, and how harmful it is. Now, it’s time to kill the virus. But removing the black algae is not a piece of cake. You have to burn a lot of wood and straw to kill them. 

Here is the step-by-step guide you can follow & apply to remove the black algae from your saltwater pool. 

  1. Begin with cleaning the pool filter. Having black algae in your pool means there is algae in the filter also. So, backwash the filter and wash it away with clean water. You can use the filter cleaner if it is difficult to remove the algae. 
  1. Once you clean the filter, it’s time to scrub the affected area heavily. Use a stainless steel brush and brush away the algae spot from the ladder, pool liner, and anywhere it grows. If the algae mark is stubborn, wear rubber gloves and rub the affected area vigorously. 
  1. As we said before, getting rid of the black algae is not simple. So, you need to shock your pool by applying 3x sodium dichloro compared to the amount you usually use. For example, 1 pound of sodium dichloro is ideal for 10000 gallons of water. So, you need 3 pounds to shock a pool that contains black algae. 
  1. Apply the proper amount of algaecide into your pool according to the instruction written on the product package. 
  1. Run your pool filter to circulate water. We recommend you run the filter for 24 hours to 48 hours. 
  1. After shocking the pool, if there is still black algae or black spot, brush your pool again with a stainless steel brush.  Then, re-shock your pool. And this time, apply a regular amount of sodium dichloro. Next, start the pool filter and let it run for the next 24-48 hours.


  • Are black algae in the pool dangerous?

Honestly, the presence of black algae in your pool can’t make you sick. But black algae contains harbor organisms like E-coly, and this harmful bacteria would cause illness.  

  • What causes black algae in the pool?

Hot temperature, unbalanced water, and malfunctioning filtration system are responsible for growing black algae in your saltwater pool.

  • Is it okay to swim in a pool that has black algae?

Yes, it is okay to swim in a pool that contains black algae as it can’t cause illness alone. However, most swimmers don’t like to swim if there is black algae in the pool. But you should be careful enough so that you don’t drink the infected water. 

  • How long does it take to get rid of black algae in the pool?

It takes a minimum of 24 hours to get rid of black algae after shocking your pool. During this time, you must run the pump for 24 hours. 


Black algae in the saltwater pool make the water infected and unsuitable for swimming. As black algae is a bacteria, it is toxic and contains E.coly, making you sick.  

Though removing black algae from the pool is challenging, the guide we mentioned above will help you kill the virus. So, apply the step-by-step process and bring back the natural look of your pool to enjoy the hot summer.

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