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How to Clear Up a Green or Black Swimming Pool

Updated on October 19, 2016
Barack James profile image

Barack is a chemical engineer and pool water chemistry nerd. He has been in the commercial pool maintenance industry for more than 7 years!


A green or black swimming pool normally forms due to poor pool sanitization or chlorination (also known as pool shocking). As a result, algae and other harmful bacteria thrive in the swimming pool water. Algae forms mainly in hot and humid climates or during the summer, simply because chlorine reduces as water temperature increases.

But don't think, even for a moment, that maintaining only chlorine levels is enough. You need to keep an appropriate balance of all chemicals in the pool. Most chemicals used in the pool, such as pH and sanitizer, will affect how chlorine works. For this reason, the only perfect way to avoid having green, black, or cloudy pool water in the future is to achieve chemically balanced pool water.

A green swimming pool will cause a number of health hazards ranging from skin coating and slippery floors to harmful bacteria growth and rescue prevention. Healthy swimming pool water should be a tinted blue color and not any other color.

Checklist of Items needed for Clearing up a Green Pool Water

Here is brief checlist of all that you may need to clear up a green swimming pool:

  1. pH adjusting chemicals
  2. Chlorine shock
  3. Agaecide
  4. Vacuuming machine
  5. Backwash hoses
  6. A working swimming pool filter system
  7. A large leaf net
  8. Accurate swimming pool water test kit

5 Essential Steps for Clearing Up a Green Swimming Pool

Now that you have all the necessary chemicals and equipment for clearing a green swimming pool, you need to begin troubleshooting the pool water one step at a time until you end up with blue water.

This is a long process and cannot be achieved in a day or two.

Step One: Remove Large Debris

Large and visible debris should be dealt with first. Here, you will need to use a large leaf net instead of the hand skimmer.

Note: A large leaf net will stir up the entire pool water and move debris that has settled beneath the pool. As a result, the pool water may look dirtier, but it will eventually settle down with time.

Step Two: Vacuum to Remove Small Particles

As a warning, be cautious not to use a vacuuming equipment if the pool water still has large debris floating or settled at the bottom of the swimming pool. This will block your underground pipes and filter.

Note: Only vacuum your swimming pool when you can clearly see the bottom of the pool to ensure that no large debris still remain.

Step Three: Correct the pH Level

Your swimming pool may still be green, but free of large debris and small particles. At this stage, you need to test and establish the pH level before adding any pH solution. A pH level of 7.4 ppm to 7.8 ppm is fine. Anything above or below that needs attention.

Use the pH Plus (pH Increaser) to increase a pH level lower than 7.4 ppm. On the other hand, use pH Minus (pH Reducer) to decrease a pH level higher than 7.8 ppm. Ensure that the pH level is within the correct range, or else the swimming pool water will not clear up.

Step Four: Shock the Swimming Pool

To shock the swimming pool, you chlorinate the water to kill algae and any bacteria that is present. I like using liquid chlorine, preferably sodium hypochloride . It works much faster than the powder counterpart.

Note: It's important to mention that this is an experimental process, therefore results will not appear after one day. Clear water is usually achieved after two or three days of correct chlorination. If you feel that you need to use more chlorine, don't use a large amount in one go. Use the chlorine in a range of 3 or 4 gallons to start and wait to see if the pool clears up. If the first chlorination makes little to no change, add another 3 or 4 gallons of chlorine the following day.

Remember, this is a normal method used to raise free chlorine levels. Because a swimming pool cannot be over-shocked, you can add more and more chlorine every day until the swimming pool water totally clears up. If you find yourself in this stage, you may need to add algaecide to help kill the algae faster.

Chlorine levels in the pool water may be high as a result of this process, however, it will reduce with time. Don't worry too much. The main thing here is to focus on the clarity of the pool water.

Step Five: Run the Filter 24 Hours a Day

The more you run the swimming pool filter the faster the water will clear up. Also, remember that green or dirty swimming pool water will clog the filter system more frequently during this process, particularly the DE and Catridge pool filters. As such, you need to backwash your filter everyday to ensure that the filter operates effectively during the process.

Note: The more the filter runs and the more it is backwashed, the faster the swimming pool water will clear up.

Also, if you have the DE filter, this process may be shorter since the DE filter is more efficient in clearing up pool water than the sand or Catridge counterparts. If you use a DE filter, remember to add a new DE substance after every backwash to speed up the clearing process.

In addition, whichever filter you are using, ensure that your pool filter system is functioning properly. If the filter system is not working properly, the pool water will never clear up after all these efforts, and you will have to replace or repair the filter.

A Clear Tinted Blue Swimming Pool Water

A cleared swimming pool will be blue in color; while a clearing pool water will be light green or cloudy white
A cleared swimming pool will be blue in color; while a clearing pool water will be light green or cloudy white | Source

Important Information to Learn Before Proceeding

Chlorine levels:

  • Free chlorine (added chlorine) is the substance responsible for attacking bacteria and other contaminants in the pool water. As the free chlorine is used up, combined chlorine (or chloramine) is formed. Combined chlorine cannot kill bacteria and other harmful organisms thriving in the pool water. The higher the combined chlorine in the pool water, the higher the chances of having a green or cloudy pool water.
  • There are a number of chlorine shocks you can buy. Whichever chlorine shock you choose to use, ensure that free chlorine is always maintained at 3 ppm.
  • It is recommended to maintain combined chlorine always below 0.5 ppm or at 0.0 ppm, if possible. To reduce chloramine levels in the pool water, the affected swimming pool should be shock chlorinated.
  • If you have an outdoor swimming pool, you can use Cyanuric acid as chlorine stabilizer to help prevent UV rays or hot water temperatures from consuming free chlorine at higher rates.

pH Levels:

  • Ensure that you maintain the correct pH level of your pool water. It should always be between 7.4 ppm and 7.8 ppm with 7.6 pmm being the most ideal level.
  • To control the pH, use either pH Plus (pH Increaser) such as muriatic or sulfuric acid, or use pH Minus (pH Reducer) such as soda ash to add or to reduce the pH balance respectively.


  • When total alkalinity increase out of range (between 80 ppm and 120 ppm), pH and calcium will significantly increase to destructive to levels.
  • Ensure that you lower total alkalinity to recommended levels when out of balance to avoid issues with pH and calcium scaling.
  • It is always essential to frequently test your pool water and take chemical readings to ensure that water is chemically balanced. If possible, pool water test should be done on a daily or weekly basis depending on which chemical you are testing.
  • Rather than guessing the pool chemical level by matching colors with several brands of test strips, I use a digital pool water test kit. If you can find an accurate and easy-to-use pool water test kit like the LaMotte ColorQ Pro 7, this will save you a lot of time as it is easy to use and very effective for a frequent swimming pool water testing purposes. It contains a number of tests including pH, free, combined, total chlorine levels, Bromine, calcium hardness, total alkalinity, and Cyanuric acid. Here is a complete review of LaMotte ColorQ Pro 7 digital pool water test kit.
  • To avoid troublesome pool mathematics, after getting the correct values of all chemicals in the pool, I use a pool calculator to find appropriate amounts of pool chemicals to add into the pool. How easy could pool chemistry get?


  • Your filtration and circulation system plays a very important role in pool maintenance. A faulty pool filter and poor circulation system will cause dirty and stagnant water, which may bring about green or cloudy pool water.


  • You need to ensure that all pumps are working properly. Regularly clean, change, and backwash your pool filter when needed.

Which Pool Water Test Kit do You Use?

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This comprehensive DIY guide should work effectively for your green swimming pool. It is also important to note that maintaining a swimming pool is cheaper than the cost incurred when it turns green, black, or cloudy.

To maintain your pool, ensure that you have all the swimming pool maintenance equipments and chemicals, and that you regularly check the levels of all chemicals in your pool before it gets out of hand.

Swimming Pool maintenance

How regularly do you check and maintain your swimming pool status?

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