How to Get Rid of Black Algae in Your Pool

You’ve opened your pool up to find black algae growing. This is a pool owner’s worst nightmares, but all is not lost. Algae growth is a sure sign that something has gone wrong with your pool maintenance, but sometimes it happens.

What you need is to understand what this invader is, how to get rid of it, and how to prevent it from taking over again. This article will provide you with a thorough understanding of black algae and a step-by-step guide to keeping your swimming pool black algae-free.

How to Get Rid of Black Algae in Your Pool

What Is Black Algae, And Why Is It So Bad?

Black algae are living organisms. If you don’t take care of the problem quickly, it can easily take over your swimming pool and begin causing damage. Black algae is particularly hard to get rid of because it roots in cracks in the cement. It has also developed a protection mechanism, so it’s resistant to chlorine.

Any form of algae will be prone to grow in your pool if it has a high pH level, low chlorine levels, poor circulation, or poor filtration. On hot sunny days, algae thrive.

Black algae looks scarier than other types of algae due to their color, but you’ll be surprised to hear that it’s not harmful to humans. The health risks of algae infestation come with the bacteria that breed with it.

Before you engage in an intensive cleaning process to rid your pool of black algae, make sure that’s actually what you’re dealing with. Here are some ways to tell that you have black algae in your pool:

  • Black or blue-green spots with raised heads that are not free-floating in the water. Free-floating varieties of algae are the green and mustard varieties.
  • The black spots are on rough surfaces in your pool.
  • You can’t easily brush off the spots.
  • You have ensured proper sanitizer levels and filtration, but the spots are still there.
  • It’s not staining your pool wall, which can be scraped off.

How To Stop Black Algae from Growing In Your Swimming Pool

The best cure for black algae is prevention. It’s going to take you hours to get rid of it once it’s there, so preventing it will save you a lot of time and effort.

  • If you’ve been swimming in a lake or ocean, wash and dry your swimsuit before entering your swimming pool. The ocean is a common source of black algae being transferred into a pool because the algae spores stick in your swimsuit, then jump off in your pool water.
  • Maintain proper pool chemistry. Check and regulate the levels of chemicals in your pool on a regular basis. Fluctuations in pH, chlorine, and alkalinity can give algae the opportunity to bloom.
  • Filter your pool and run your pump regularly. Your pool pump should be on for 8-12 hours each day to help catch any spores in your filter.
  • Regularly vacuum and brush your pool.
  • Clean and sanitize pool toys and equipment that are used in the water.
  • Shock your pool once per week to kill off organic contaminants. In addition, the super chlorination process should help kill off spores that are resistant to regular chlorine levels.

Using an algaecide regularly is recommended to prevent problems if your sanitization program fails. Heavy rainfalls or high swimmer loads can quickly dissipate your supply of chlorine or bromine if you’re not on top of it.

Having algaecide as a backup will help you keep algae at bay, even if your sanitizer levels drop for a period of time. Think of the algaecide as a form of insurance for when your sanitizer isn’t enough.

Removing Black Algae from Your Pool

If you’ve been caught off guard and already have black algae growing in your swimming pool, it’s time to roll up your sleeves and get to work. Here is the step-by-step process for getting black algae out of your pool.

Materials required: pool brush, pool shock, algaecide, chlorine tablets, granular chlorine

Get Rid of Black Algae In 11 Steps

1. Clean and sanitize your tools

Before getting started, make sure to sanitize all the tools you are going to use to avoid adding more algae spores into your pool. Spraying and scrubbing your tools down with a chlorine solution should do the trick.

2. Clean your filter

Even if you can’t see it, there are definitely algae spores in your filter if there is algae growing in your water. Follow your manufacturer’s directions for filter cleaning, or backwash your sand or DH filter.

3. Scrub your pool surfaces

You’ll need to use your pool brush to scrub the sides and bottom of your pool until there is no more algae attached. Then do it again to get all the stuff you can’t see!

If you have a vinyl-lined pool, you’ll need to use a softer bristled brush than for a cement pool.

4. Scrub your pool with chlorine tablets

You probably want to wear gloves to complete this step. Next, take a tablet of chlorine and scrub your pool walls and bottom with it. It works best if you break a tablet in half and use the rough side to scrub with. The chlorine will penetrate any cracks and kill the algae spores hiding within them.

5. Shock your pool

Shocking your pool will kill off any leftover bacterial growth in your water. Make sure you use a super shock chlorine treatment and follow the manufacturer’s directions for use. However, a good rule to follow is to super chlorinate your pool water to a level of 30 parts per million (ppm).

Super chlorination will break down the DNA in molecules of algae to prevent them from growing or reproducing.

6. Add extra granular chlorine

Be generous with chlorine in areas that you scrubbed off black algae patches.

7. Add algaecide

A single bottle of algaecide will treat 15,000 gallons of pool water. After you have cleaned the existing algae out of your pool, add this to prevent future outbreaks.

8. Run your pool pump

Give your pool 24 hours to settle with the extra chemicals, then run your pump for another 24 hours. After that, it should be run for 8-12 hours per day for the rest of the season.

9. Brush your pool surfaces

For the next few days to a week after the initial cleaning, you will want to brush your pool 2-4 times a day. This will remove spores as they creep out of small cracks.

10. Clean your filter (yes, again)

Each time you brush your pool surfaces, you release spores into the water that are then sucked into your filter. You’ve removed them from the pool, but they can live on your filter for quite a while, so clean your filter regularly. If you have a DE or sand filter system, this will mean regular backwashing.

11. Re-check for black algae

If you have a stubborn algae infestation, you may notice black spots creeping back in once in a while. Each time this happens, brush the spots off and shock your pool.

Black algae is the most difficult type of algae to get rid of. If you can’t get the infestation under control, you may need to consult a professional.


If you have had to remove black algae from your swimming pool, you will realize how difficult a task this is to complete. You can avoid heavy algae infestations by performing regular pool maintenance such as brushing surfaces, vacuuming, maintaining chemical levels, and cleaning your filter.

Running the pump on a daily basis will also help keep yucky bacteria out of your water. It doesn’t have to be difficult to keep your pool water clear if you stay on top of it.

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