How to Clean a Green Pool

a pool with a boat and trees.

If your pool is full of green water, you know that you have to take care of the problem that is causing it before anyone can enjoy being in the pool! A green pool looks gross and can seem to happen overnight. Don’t fret! You can correct it, usually within a few days. Our experts at Prestige Pools of NC have written this article to explain why your pool has turned green and what you can do to get the water crystal clear again.

What Has Caused My Pool to Turn Green?

The most common reason a pool turns green is due to algae growth, which contains chlorophyll. Chlorophyll causes the water to turn green. Exactly what is algae? Algae encompasses a wide variety of aquatic plants–any plants that use chlorophyll as their primary photosynthetic pigment. Algae uses the sun, water, and carbon dioxide to make food. They bond to the walls, floor, and steps of a pool and even float in the water. Algae grow quickly and multiply. The algae aren’t harmful generally but harmful bacteria like E.coli, parasites, and salmonella can exist in it. 

Black algae, on the other hand, is a significant health risk. You can learn what to do if you get black algae in your pool here.

Note that if you don’t have signs of algae, another reason your pool may be green could be due to metals that are dissolved in the water. In this case, you will need to check the pool pH to make sure metal components such as railings and ladders aren’t corroding.

Why Have Algae Grown in My Pool?

Algae grow when the water chemistry and pool filter aren’t as they should be. Chlorine kills algae and prevents them from growing. The filter collects any particulate like algae and algae food and removes them from the pool water. When the chlorine level is too low, there isn’t enough to kill the algae so they start to grow.

Steps to Correct a Green Swimming Pool

Step 1: Check the Chemicals in Your Pool

The most important numbers are your free chlorine and pH. More than likely, if you have an algae problem, your chlorine is extremely low. Using test strips or a liquid test kit, test the pH and alkalinity levels. The pH level should be between 7.4 and 7.6. The alkalinity level should be between 100 and 150 ppm (parts per million). If the pH and alkalinity levels are a bit low, don’t worry too much. You will raise these when you shock the pool later.

Step 2: Check and Clean the Filter

Clear out any debris from the skimmer basket such as leaves and twigs. Put in new nets to be sure there is no algae lingering. Backwash your sand or cartridge filter for a couple of minutes. After cleaning the filtration system, it should be able to work at the maximum flow rate and will be able to handle water problems more efficiently.

Step 3: Shock the Pool Water

Shocking the pool water is simply putting an abundance of chlorine in the water. In effect, you are over-chlorinating it. This process kills the bacteria that causes algae. Turn on the pool pump so the water is circulating. Increase the chlorine level by adding up to 5 times the normal amount. Read the instructions for your particular product and be sure to calculate the amount for the size of your pool. Then, by walking around the pool, spread the shock (chlorine) all over the pool, not just in one spot.

Step 4: Add Algaecide

After 24 hours, add algaecide to prevent algae from growing. Algaecide works with the chlorine sanitizer to keep the level balanced. But, if you put it in either when you shock the pool or too soon after, you can create bad chemical reactions.

Step 5: Cleaning the Pool

To get the pool clean, you will need to get all of the dead algae out of the water. After the algae die, they lose their green color. But, if they are left in the pool, they make the water cloudy. Follow these steps to clean the pool thoroughly.

  1. Continue to run the filter for about 24 hours without stopping in order to clear out the floating algae.
  2. Brush the walls and the floor of the pool to loosen and remove algae from the pool vinyl liner.
  3. Vacuum the bottom of the pool to get rid of dead algae that sink to the bottom.

If there is a lot of algae bloom, it can take a few days to get the pool water back to normal. Regular brushing and vacuuming with the filter running 24 hours a day will clear the water in no more than five days.

Step 6: Repeat Brushing the Pool, Vacuuming, and Cleaning the Filter

You may need to brush the surfaces, vacuum, and clean the filter again. This is especially true if you have black algae because it is difficult to remove. If algae is left on surfaces, new algae will grow back in the same place.

After you have a clean pool with crystal clear water, you will need to keep an eye out for more algae growth. Refer to our articles, “How to Keep Your Pool Looking New,” “Tips to Caring for Your Pool,” and “How to Keep Your Vinyl Pool Clean” for practices to ensure your pool is in great shape for the entire season!

Contact Prestige Pools of NC for a Vinyl-Liner Pool

Are you thinking about building an in-ground vinyl-liner pool? If so, contact our experienced team at Prestige Pools of NC. We can help you look at all the options for building a pool that is unique and a beautiful addition to your backyard where friends and family can gather for fun and entertainment! Our team will work with you to make your vision come to life. Call us today at 919-586-8556 or fill out our online contact form to schedule a quote for a vinyl-liner pool installation in Clayton, Raleigh, Coats, Garner, Holly Springs, Fuquay-Varina, Middlesex, Wendell, Zebulon, or the surrounding areas.