Defeating Algae!

Planning an end of summer party and suddenly discover your pool water is green? Are you the kind of person who constantly has green pool water no matter what you do? Does it seem like there is no way to get rid of the algae in your pool?

Well you are in luck, because we are here to help you out...

Know Your Enemy

Swimming pool algae is a small plant organism that likes to grow in warm, dark, unsanitized water. The most common pool algae is green in color and spreads very fast. You’ll need to act quickly and always be on the lookout for an algae outbreak.

The strength of algae is determined by color. If your pool is a teal color, it means you’ve caught the algae at an early stage of growth. It has not taken over your pool yet, and should be easy to overcome with a few simple steps.

If your pool is dark green or black, you have a stronger type of algae to defeat. This algae is more powerful and has taken over your pool.

Algae Self-Defense

You can easily defend yourself against an algae attack using the right sanitizer. This is your secret weapon. Algae cannot grow in water with a proper level of free chlorine.

Algae is also likely to cling to the surfaces of your pool and work its roots in deep. Dark places, small cracks and crevices is where you’ll find them beginning to bloom.

Don’t let algae make the first move. Here are some methods you can use to keep your pool clean:

  • Keep the walls and floor of your pool clean by brushing the pool with a standard pool brush attached to a telescopic pole.

  • Vacuum your pool once or twice a week (more if needed).

  • Skim the surface of your pool water everyday.

  • Run your filter and pump for 8 to 12 hours per day.

  • pH should be between 7.4 and 7.6.

  • Alkalinity should be between 100 ppm and 150 ppm (parts per million).

  • Free chlorine level should be at 3 ppm.

  • Use a weekly dose of algaecide.

How To Defeat Algae At The Source

If you are unsuccessful at fending off algae, you must now fight the algae at the source. You will need the proper tools:

  • A 5 gallon bucket of water

  • Calcium hypochlorite pool shock

  • Wooden paint stirrer

  • Gloves

  • Protective eyewear

  • Clothes you don’t care about

Determine the type of algae you have by the color of the pool. If your pool is a teal color, you will need to double shock it. This means using 2 pounds of shock per 10,000 gallons of water.

If your pool is green or dark green, triple shock it by using 3 pounds per 10,000 gallons. And if you pool is black, you will need to quadruple shock your water by using 4 pounds of shock per 10,000 gallons of water.

Prepare to Fight

The best time to attack the algae is at dusk or nighttime. This will allow the chlorine shock to be the most effective. 

Put on your old clothes, gloves, and protective eyewear. You will be handling a very concentrated chlorine solution which could bleach what you’re wearing, hence the need for old clothes and protection.

Turn on your filter system and take it off the timer (if you have one). You will need to run your swimming pool 24 hours a day, and 7 days a week, until the algae is conquered and the water is clear.

Now that you’ve prepared yourself, it’s time to get to work. This technique is called, “The Pre-Dissolve.”

  1. Fill your 5 gallon bucket with warm water or pool water.

  2. Pour in ONLY 1 pound of chlorine shock carefully.

  3. Slowly stir the shock into the water with a wooden paint stirrer. Avoid splashing.

  4. Take the shock mixture and slowly pour it around your swimming pool. 

Repeat these steps until you have added all the necessary pounds of shock to your water.

Allow your pool to run overnight and check it the next morning. If your pool has turned a cloudy blue color, you have successfully destroyed the algae. If the pool is still a green color, repeat the steps until completely gone. Brush, vacuum, check your chemicals, and re-shock the pool with the amount of shock you need for the new color. 

Once your pool is cloudy blue, you’ll need to continue to run your pump and filter until the water is clear. You can clear it faster by using a liquid clarifier chemical.


Adapted from Swim University - 


Matt Giovanisci is the creator of Swim University and has over 15 years of experience in the swimming pool and hot tub industry. He is also an award winning web designer and has been featured on Martha Stewart Radio as a pool & hot tub expert.