How to Prevent and Treat Algae Growth in Your Pool

Typically, three main varieties of algae grow in swimming pools. They come in a variety of colors, including green, yellow (mustard), and black algae. Green algae is the most common and can cause your pool water to seem hazy and greenish. Yellow algae are more persistent and can cling to the walls and floor of your pool, whereas black algae are the most difficult to remove, developing a thick protective outer coating while also being deeply rooted into your pool’s surface.

Algae spores can find pretty creative ways to get into your pool… dirt and leaves can blow into your pool on windy days.  And even rain, your swimwear or pool equipment can become a source. They rely on sunlight, warmth, and nutrients like phosphates and nitrates, which can originate from fertilizers, leaves, and other organic material once they're in the water.

Keeping Algae at Bay

The best strategy is to keep it from growing in the first place. This is not that difficult to do if you follow just these guidelines:

Maintain Proper Water Chemistry: Keeping pool water balanced (especially pH and chlorine) is essential for preventing algae growth. Test your pool water frequently and regularly so things don’t get out of control (at least once a week) to ensure that the following levels are maintained:

• pH: 7.4-7.6
• Alkalinity total: 80-120 ppm
• Calcium hardness ranges between 200 and 400 ppm.
• Chlorine: 2-4 parts per million
• Cyanuric acid concentration: 30-50 ppm

Keep Your Pool Clean: Try to skim leaves and debris from your pool’s surface on a daily basis to reduce the nutrients available to algae. Without nutrients, they can’t grow.  Brush your pool walls and bottom at least once a week to remove any potential algae spores and keep them from growing.

Vacuum Your Pool: Once a week, vacuum your pool to remove dirt, debris, and potentially harmful algae spores that have fallen to the bottom. You have a much better chance of eliminating the possibility of algae growth when there’s less organic material in your pool.

Maintain Your Pool Filter: Your pool filter is an important piece in eliminating algae spores from the water. To ensure appropriate water circulation and filtration, run your pool filter for 8-12 hours every day.  A general guide for residential pool’s is to have the water “turn over” at least once a day.  During the summer months or on occasions  where your pool has been used more than normal, you may want to run your pool’s filter even longer so you get even more “turn over”.

If you do see the beginning of an algae bloom in your pool follow these steps to treat it:

Before starting to treat the algae, test and balance your pool water again to verify it is properly balanced.  See the lists of tests above.  Adjust the water chemistry as needed, paying close attention to pH and chlorine levels in particular. Algae flourishes in high pH conditions, so reducing the pH to the lower end of the pH range, roughly 7.2 can aid in inhibiting their growth. Also, check that the chlorine level is between 2-4 ppm.

Brush the Pool: Using a pool brush, you want to vigorously scrub your pool's walls and bottom, concentrating on areas with obvious algae growth. This will help dislodge the algae from pool surfaces while also exposing them to pool chemicals for more effective treatment.

After brushing, you may need to shock your pool with a higher than normal concentration of chlorine or a non-chlorine shock solution. For the best results, use an algaecide or an extra-strength pool shock. Follow the manufacturer's recommendations for dosage and application method. Depending on how bad the outbreak is, you may need to shock your pool multiple times to completely remove the algae.

Run Your Pool Filter: To help get rid of the dead algae and other particles from the water, run your pool filter constantly for 24-48 hours. To ensure proper filtration, backwash or clean your filter as needed. To guarantee best performance, if your pool filter is cartridge-based, you may need to clean or change the cartridge more regularly during algae treatment.

You’ll notice that the dead algae may drop to the pool bottom.  After the dead algae has settled, use a pool vacuum or automatic pool cleaner to remove it from the pool's bottom. To prevent persistent algae, such as black or yellow algae, from recirculating back into the pool, vacuum the pool to waste.

Keep a closer than usual check on the chemistry of your pool water during and after algae treatment. To help keep the appropriate balance, test the water on a daily basis and make any required adjustments. Brush and vacuum the pool as needed to ensure that the algae is completely removed.

Prevent Future Algae Growth: After the algae has been removed, use the prevention tips described earlier in this article to reduce the possibility of future outbreaks. You may want to consider including an algaecide in your regular pool maintenance regimen, especially during periods of high temperatures or extensive use, as these conditions can stimulate algae growth.

Finally, avoiding and controlling algae growth in your swimming pool is critical for keeping it clean, safe, and enjoyable. You can efficiently keep algae at bay and enjoy crystal-clear water all season long by regularly testing and balancing your pool water, cleaning your pool, and using the proper pool chemicals.