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The Home Depot

Why is My Pool Water Green?

Pro Referral > Home Guides > Pool and Hot Tub > Why is My Pool Water Green?
Why is My Pool Water Green?

When you enjoy the recreation of a backyard swimming pool, this aquatic feature requires ongoing maintenance and monitoring. The quality of the water in the pool must be clean and free of bacteria to keep the people who use your pool from harm. If your pool water becomes green, other issues can occur as well.


Not only could you be exposing swimmers to bacteria, but green pool water is also a prime location for mosquito breeding. Most communities require residents to take reasonable steps to prevent mosquitoes from breeding on a property.


As you maintain your pool, if you detect green pool water, learn the cause behind the water issues and resolve them quickly.

  1. If you use products that contain a high percentage of phosphates and nitrates, you can contaminate the pool and cause algae to take hold.


    Algae are plants that grow naturally in water. To grow, algae uses photosynthesis to create food. Although many different types of algae exist in assorted colors, green algae is the most prevalent algae that occurs in pools. The green color that can occur from algae may vary from dark green to yellowish green, and even to a bluish green at times.


    When you find algae in your pool, it may make the water become hazy and cloudy. Algae may float in the water or it may coat the sides and bottom of the pool. Left to grow, algae will eventually clog pool filters and damage surfaces of the pool.

  2. 2.Causes Of Green Pool Water

    Below you'll find the most common reasons for your pool water to turn green.

    • • A pool requires ongoing maintenance to keep the water clean. This includes regular sanitizing of the water to prevent algae. If you have an increased number of swimmers in your pool, it will be important to increase the amount of chemicals you use in the water to keep it clean and free of bacteria.
    • • Another cause of algae can be vegetation and trees growing around the pool area. These trees will create an abundance of shade over the pool, which can be a problem. Decreased sunlight on a pool contributes to algae growth
    • • Be careful with the yard and lawn chemicals you use when landscaping if you have a pool. If you use products that contain a high percentage of phosphates and nitrates, you can contaminate the pool and cause algae to take hold.
    • • A significant rainstorm can also change the balance of chemicals in your pool. After a heavy shower, you may need to add more chlorine and sanitizer to keep algae from developing.
  4. 3.Preventing Green Pool Water

    Follow the methods below to ensure your pool water stays crystal clear.

    • • To prevent algae from taking over your pool, maintain the sanitizer levels properly in the water at all times.
    • • It’s also important to operate the pool filter at least 10 hours out of every 24 hours – especially when people are using the pool.
    • • Clean the pool with a pool vacuum once each week and brush all interior surfaces once each week.
    • • Use an algicide if you have issues with algae and shock the pool once each week to prevent algae.
    • • If you have recreational items used in the pool, clean these items as well so you don’t reintroduce algae into your clean pool water.

    With careful maintenance, you can diagnose green pool water and take steps to correct algae issues.

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