Algae blooms are caused by algae spores entering your pool and not being sanitized and filtered out of your water. Spores commonly enter your pool through wind, storms, items, or swimmers entering the water.

There are three types of algae common in pools: green, mustard, and black. Green algae is the most common and also the easiest to kill. Mustard algae (also known as yellow algae) is commonly mistaken for dirt at the bottom of the pool. This form of algae normally grows on shady areas of the pool and killing it requires an extra chemical such as Yellow Out in addition to chlorine. Black algae is the least common, and also the hardest to remove. Black algae is normally found as coin-sized spots, whose roots are buried deep into the surface of the pool. Vigorous brushing and strong chemicals are required to remove black algae.

Common prevention techniques like keeping a chlorine level between 1.0ppm – 3.0ppm, brushing at least once a week, running your filter at least eight hours a night, and reducing the amount of phosphates, will all help keep algae out of your pool. These techniques though, cannot guarantee algae will stay away.


When your pool does develop an algae bloom, quick action is necessary to minimize the problem. These following steps will focus on green algae and mustard algae, as they are the most common.

1. Ensure your water is properly balanced. The most important reading is pH. If just using shock, your pH should ideally be between 7.4 and 7.6. This optimizes the sanitizing power of the chlorine in your pool. However, if using Green to Clean or Yellow Out, Leslie’s recommends pH at or above 8.0.


2. Check your filter to make sure it is working properly. If you discover any problems or need to clean the filters, do it before treating the algae. Without proper filtration, the algae will not be able to be removed from the pool.

3. Thoroughly brush the pool. This will help remove algae from surfaces, where it is more difficult to treat.


4. Apply a chlorine-based shock to your pool such as Power Powder Plus, Chlor Brite, or Liquid Chlorine. Always follow the package directions. When applying chlorine to treat algae, the ideal time to apply the chlorine is in the evening. This prevents the sun from burning off chlorine that otherwise would be used to sanitize the pool.


5. If you have mustard algae in your pool, use a product such as Yellow Out in addition to chlorine to help kill the bloom. Yellow Out requires 2lbs. per 15,000 gallons of pool water. For green algae, a product like Green to Clean may be helpful to add in addition to the chlorine. When adding these chemicals, make sure to wait five minutes between adding the chlorine and either Yellow Out or Green to Clean.

6. Run the pool for 24 hours.

7. Backwash or chemically clean your filter.

8. Once the chlorine has fallen below 5.0ppm, add an algaecide such as Leslie’s Algae Control, and then brush the pool again.


9. The water may be cloudy after treating the pool for algae. This is normal and should go away by running the filter and cleaning it after the pool has been running for 24 hours. If cloudiness still persists, continue running your filter and apply a clarifier such as Ultra Bright. This binds small particles in your pool together and allows your filter to remove them effectively.


10. Continue to run your filter until the pool is clear. If algae or cloudiness continue to exist, repeat this treatment until the algae is gone. Higher dosages of chlorine may be recommended. A local Leslie’s professional can further advise you on the correct amounts.

11. Bring a water sample into a local Leslie’s store once the algae is removed. Correctly balancing your water will help prevent algae in the future and keep your pool looking sparkling clean.


Keeping algae out of the pool is not only a season-long process, but for some it’s a year-long process. Despite your best attempts, algae may still bloom in your pool. If that happens, these steps will help clear up your pool in no time.