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How to Identify, Treat, and Remove Algae in Your Swimming Pool

How to Identify, Treat, and Remove Algae in Your Swimming Pool

Pool Maintenance

Pool algae on pool stepsDuring the months of July and August, algae can be a very big problem for swimming pool owners. With the higher temperatures during these months, as well as inconsistency in a pool's sanitizer levels, algae can rear its ugly head.

Algae is a single-celled plant form. It uses the process of photosynthesis to manufacture its own food. It comes in a very wide variety of colors and forms, making it adaptable to almost any condition.

Due to algae's microscopic size, it takes literally millions of these plants to accumulate to be noticed by the naked eye! By that time it may be too late and very costly to correct. 

As we tell all our customers: The best way to eliminate algae is through prevention! (This is also why we are such proponents of salt water chlorine systems.)

This article will discuss the different types of algae and how to deal with each.

What are the types of algae, and how do you remove them?

  • Green algae can cling to the wall or float in the water. Get rid of it by brushing the pool, shocking, and adding Algaecide 60.
  • Black algae looks like black spots and feels slimy. Get rid of it by aggressively brushing the algae and adding Algaecide 60.
  • Mustard algae looks like sand in the bottom of the pool. Get rid of it by aggressively brushing the algae and adding Algaecide 60.
  • If the pool is full of algae, add a flocculant (floc) to the water and vacuum up the coagulated algae that settles on the bottom of the pool.

Green Algae

The most common form of algae in swimming pools is "green" algae.

Green algae varies in color from blue-green to yellow-green to dark-green. It can be free floating in the water (turning the water a hazy green) or can cling to the wall-clinging (patches of green).

Green algae can be treated fairly simply with the right amount of brushing, shocking, and algaecide.



Properly analyze the pool water to ensure the pH is at the proper level. Balance the water chemistry if needed.

Pools treated with chlorine should be brushed thoroughly, then shocked, raising the chlorine levels above 3 ppm.

Also, add a strong dose of Algaecide 60 to the water. Continue to check the pool's filtration throughout this process to ensure proper water flow.

You may have to repeat this process a few times in order to eradicate the algae 100 percent.

Black Algae

"Black Algae"  is actually blue-green algae. It forms in cracks and crevices on pool surfaces, especially plaster finishes.

We normally find black algae growing in, but not limited to, shady areas of the pool. Black algae is more typically found in concrete or plaster finished pools because of their rough surfaces.

It is known for a heavy slime layer and "skeletal growths" that make it impervious to normal chlorine levels.

Black algae usually doesn't change the water clarity. It just makes your pool appear to have black spots on the surface.



Properly analyze and balance the water.

Prior to and during treatment, you MUST thoroughly brush the algae in order to "break open" the slime layer. This is a critical step. If you skip it, you'll prevent the treatment from working.

Shock the pool very aggressively and continue to brush the black algae. Add substantial amounts of Algaecide 60.

Mustard Algae

Mustard algae is a chlorine-resistant form of green algae (yellow-green to brown in color).

It often resembles dirt or sand on the bottom or sides of a pool.



Same as black algae.


In certain cases, when a pool is full of algae, you have to vacuum the algae directly out of the pool.

You can do this by brushing the algae off the walls, then adding a 'floc' to the water. It coagulates the algae and causes it to settle. Once it settles, vacuum it directly out of the pool.

When attempting to floc a pool, follow the directions on the bottle very carefully.

Hopefully you will not be burdened with algae in your swimming pool this year.

As I mentioned earlier in the article, salt chlorine generators are the best way to prevent algae in your pool. They produce a consistent feed of natural chlorine into your pool all the time. They will also allow you as a pool owner to leave for a few days without being too vigilant of your pool, but still come back to a crystal-clear, algae-free body of water.

I'm always amazed at how many pool owners think that algae a standard part of swimming pool ownership. This clearly does not have to be the case, as we have many customers at River Pools who have never even seen algae in their swimming pool. Of course, this is also why just about every one of our customers uses a salt chlorinator.

Good luck and happy swimming!

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Up Next: 

How to Get Rid of Algae in an Inground Swimming Pool

The Ultimate Guide to Inground Swimming Pool Maintenance


Editor's note: This blog article was originally published in August 2009 and has been updated and revamped for accuracy and appearance.