Pool Algae and How to Kill Any Type and/or Color

discolored pool water

When you’re ready for a refreshing afternoon dip in the pool, the last thing you want to dive into is murky water. But just what is causing that icky water? Pool algae.

Keeping water clean and sparkling is the goal of every pool owner — so when something comes along to threaten that cleanliness, it’s important to find a solution as soon as possible.

Trust the experts at ASP - America's Swimming Pool Company when we tell you that this is not something you can simply skim away! Under the right conditions, algae will begin to grow quickly, and if left untreated, you’ll find yourself with something that looks more like a pond than a pool.

Read on to learn more about this aquatic plant and how to get rid of algae in pools for good.

What Causes Pool Algae To Form

Like pollen and mold, algae spores are all around us. They utilize the sun, water, and carbon dioxide to photosynthesize and create their food, making a still body of water, like your pool, an easy target for growth.

If your pool has low chlorine levels, a pH imbalance, a dirty filter, or poor circulation, algae spores will settle in and quickly begin to multiply across the water’s surface, along the pool walls, and up stairs and ladders.

Another way algae can begin to take over your pool is through contaminated objects. If you recently spent time in a lake or river, pool toys and swimming suits used may have picked up some algae hitchhikers.

What Problems Can Pool Algae Cause and Why You Should Remove It

We are often asked: Is pool algae harmful? The answer is yes.

Algae can cause a number of problems for your pool. Most obviously, the green water is an eyesore. Combined with other pollutants and dirt, algae has the potential to stain surfaces.

Additionally, an abundance of algae raises your pool’s pH levels, creating the potential for calcium and scale-like growth across walls and stairs. Over time, this scaling causes materials to deteriorate and erode, which could lead to further issues down the road.

Because of its ability to multiply quickly, algae can cause your filter to become overwhelmed and clogged. This worsens water quality and circulation, encouraging even more algae growth.

Can You Swim in a Pool With Algae?

If you can get past the discoloration and are thinking about taking a dip in your swampy-looking pool, you may want to reconsider.

While it is not harmful to people or animals, certain bacteria, like E.Coli, feed on algae and may be lingering in your water. This bacteria could cause skin rashes and bacterial infections of the ears and eyes.

So, if you’re itching to jump in the pool, it is best to wait until you’ve taken care of your algae infestation.

What Are the Different Types of Pool Algae

There are a variety of algae that may choose to make your pool their home. Each has a distinct look, requires a different method of removal, has different growth rates, and some are harder to eliminate than others. The three most common types are green, yellow (or mustard), and black (or blue-green).

Green Pool Algae

The most common and easily recognized of the three main types of algae are green algae. Recognizable by its bright green color, this type develops in three stages: teal, dark, and black green. No matter the stage, this algae spreads rapidly and coats your pool in a slimy, slick film. Luckily, green pool algae are the easiest variety to kill.

Yellow Pool Algae (Mustard Algae)

No, no one squirted the condiment into your pool at the last family barbecue! Those blobs gathered around the perimeter of your pool are yellow, or mustard, algae. This variety is rare, typically only appearing in humid climates and sticking to shadier corners and edges of your pool. Yellow algae grow slower than its cousins, but being chlorine resistant, it is harder to get rid of, and it may take multiple attempts to fully remove it from your pool.

Black Pool Algae (Blue-Green Algae)

This is where things turn dark, literally. The third type of pool algae is black (or blue-green), a breeding ground for harmful bacteria. As the very worst type of pool algae, black algae has the potential to seep into the concrete and cause structural damage to your pool if left untreated for a long period of time. It will begin as black dots scattered across the pool floor before spreading rapidly across the water.

How to Remove and Kill Different Forms of Pool Algae

With the potential to keep you from swimming, damage your pool, and create an eyesore in the middle of your backyard, it is important to do something about your pool algae problem as soon as possible. Now that you understand the different algae types let’s dive into how you can remove them.

Remember: if any of these steps fall outside of your comfort levels when it comes to pool maintenance, you can always consult with a professional first.

Check Your Pool Water Levels

At the first sign of an algae problem, begin by checking your pool’s water levels. Remember that algae tend to grow in water that has low chlorine and stabilizer, or pH imbalances. Test all three of these and promptly correct any issues — or give our team a call for help!

Turn On Pool Pump and Keep Running

Once you’ve tested and corrected any water troubles, turn on your pool pump and leave it on. Your pool pump is responsible for pulling water in and circulating it through your heater and filter, leaving you with cleaner, warmer water. This increase in movement and filtration will make your pool a less suitable place for algae growth.

Clean Your Pool Filter

As it will be working hard to remove algae and other contaminants from your water, your filter could do with a deep clean. Remove the filter cartridges and soak them in a 50/50 water and white vinegar solution. You can also completely replace the cartridges if you would rather have a fresh start.

Remove Large and Visible Debris in Your Pool

Grab your trusty pool skimmer and get to work. Leaving large debris in your pool only provides more surfaces for algae to gather and grow on. Take the time to remove sticks, leaves, toys, and tubes or pool noodles from your pool. Be sure to thoroughly clean any items before using them in or near the pool again.

Brush Your Pool Walls and Flooring

It’s time to clean, clean, clean! Some algae can be difficult to remove with chlorine alone and requires the use of a pool brush to get the job done. Brushing the walls and the floor loosens the algae and removes it from any cracks and crevices. Keep in mind that this task could take some time, as the water will likely become cloudy as you work.

Shock Your Pool

Shocking is the process of adding chemicals to your pool to raise chlorine levels and kill bacteria and algae. We recommend using a calcium hypochlorite shock to treat your algae problems. However, green, yellow, and black algae will each require their own level of shock in order to be completely killed and removed from your water.

Shock Treatment for Green Algae

When you have a green algae problem on your hands, we recommend treating it with a double dose of shock. Read the instructions included with the product and double the dosage designated for your pool size.

So How Much Shock Treatment for Green Algae?

Recommended Treatment: 2LB of Calcium Hypochlorite for every 10,000 gallons of pool water.

Shock Treatment for Yellow Algae

For the more stubborn yellow algae, up the shocking dosage to three times the recommended amount.

So How Much Shock Treatment for Yellow Algae?

Recommended Treatment: 3LB of Calcium Hypochlorite for every 10,000 gallons of pool water.

Shock Treatment for Black Algae

Finally, fight off black algae with a quadruple dose of shock. As the toughest algae to get rid of, black algae need a stronger solution than the other varieties.

So How Much Shock Treatment for Black Algae?

Recommended Treatment: 4LB of Calcium Hypochlorite for every 10,000 gallons of pool water.

Test Your Pool Water Again

Now that you have treated your pool with the recommended shock dosage, it is time to check your water again. Test your chlorine, alkalinity, and pH levels and adjust as needed to get your pool back to its ideal state. Don’t skip this step! It’s important that your levels are back to normal before you can enjoy the water once again.

Ideal Ranges

Here is a reminder of the ideal ranges for these levels:

  • Chlorine: 1.0-3.0 PPM (parts per million)
  • pH: 7.2-7.8 PPM
  • Total Alkalinity: 80-120 PPM
  • Calcium hardness: 200-400 PPM

Add Algaecide

The next step in your algae-busting journey is to add an algaecide to your pool. Algaecide products use certain chemicals to kill algae for good. As you are searching for the right product to use, keep in mind that there are different algaecides for green, yellow, and black algae.

Brush Your Pool Again

Bring out your pool brush and scrub at the walls and floor once again, taking care to reach every corner. These steps may be starting to seem repetitive, but each one is essential in making sure you have completely rid your pool of all algae.

Vacuum or Backwash Your Pool

Now it is time to vacuum your pool manually. Take your time and hit every surface thoroughly. You can also reverse the flow of your filter, also known as backwashing. This will dislodge any debris and help clean your filter.

Run Your Pool Filter

Continue to run your pool filter, allowing it to do its job and remove debris and any lingering algae from your water.

Clean Your Pool Filter Again

Give your filter and cartridges a good clean once again for a fresh, uncontaminated start!

Treating a Saltwater Pool With Algae

If you have a saltwater pool, you can treat it for algae in a similar way to a chlorine-based pool.

  1. Test and rebalance your pool water.
  2. Scrub the walls and floor.
  3. Shock the pool.
  4. Vacuum & scrub again.
  5. Re-test your water.
  6. Clean and replace the filter.

Preventing Algae Growth in Your Pool

Once you’ve gotten rid of your algae, how do you make sure your pool doesn’t become overrun by the slimy stuff again? There are a few things you can do to prevent algae growth.

Maintain Proper pH and Sanitizer Levels

First and foremost, you must keep your water levels balanced. Refer to the ranges listed above and adjust your pH and sanitizer levels as needed.

Brush Your Pool Regularly

Brushing the surfaces of your pool often will loosen any contaminants and help get them flowing to your filter. We recommend brushing your pool one or two times a week.

Check Your Filtration System Regularly

Your filter is the hero of your pool, but sometimes it needs a little extra help in order to get the job done. Check the filter regularly and clean or replace it as needed.

Shock Your Pool on a Weekly Basis

We recommend shocking your pool every week. This will fight off any bacteria or algae growth and keep the water swimmable all season.

Utilize Other Specialty Chemicals

If you want to set up a strong line of defense for your pool, there are a few chemicals that can help.

Phosphate Remover

Algae feed on nutrients known as phosphates. If your pool has high phosphate levels, the chance of algae growth is increased. A remover will help eliminate phosphates and filter them out of your pool.


Even if you don’t have a large algae issue in your pool, using an algaecide regularly will help keep it that way! Try adding algaecide to your pool once a week for optimal results and to catch any stray algae spores.

Chlorine Enhancers

Sometimes your chlorine could do with a little extra help. Chlorine enhancers, also known as sodium bromides, accelerate your chlorine levels, helping kill bacteria and algae throughout your pool.

Clean Your Pool Filter, Pump and Skimmer Regularly

Keeping up with pool maintenance and cleaning is essential when it comes to preventing algae growth. Check your filter, pump, and skimmer often and clean as necessary.

Vacuum or Backwash Your Pool Regularly

Finally, maintain a regular pool cleaning schedule. Manually vacuum weekly to reach every corner of the pool. Try to switch your filter to backwash every so often to help keep it cleaner for longer.


No matter the type of algae you have, or if you are looking to prevent algae growth from occurring in your pool, it is important to stay vigilant and maintain a regular pool cleaning schedule. If you develop an algae issue, turn to the professionals for help! Identifying your pool’s specific needs can be tricky, and improper treatments may prolong your problems.

The team at ASP - America's Swimming Pool Company is here to help you maintain a clean and safe pool year-round. If you’re looking for more information, or are in need of regular pool cleaning, maintenance, or an inspection, check out our services, or give us a call at (866) 253-0455 today!

Disclosure: While basic pool care is encouraged for swimming pool owners, it is highly recommended you consult with a professional pool service like ASP - America's Swimming Pool Company for any issues like pool algae that arise.