The Guide To Troubleshooting A Green Pool

Kenneth Wilson

After a busy week, one of the most annoying things that could happen is when you want to relax in your pool but you’re met with a sickly green pool.

Aside from not being aesthetically pleasing to the eyes, a green pool may also smell and cause harmful effects to swimmers. This makes even your pool deck or area by the pool uninviting as well. In the long run, a green pool will also leave stains in your pool walls and floor.

If you are planning to drain your pool to replace the green water - don’t. It may seem like the logical action to take, but there are other solutions to clear a green pool. Let me share with you what I learned about cleaning green pools and preventing it from turning green again.

But before we head on to learning how to remove and prevent algae, you might want to know what causes a green pool.

Why does a Pool become Green?

Green pools exist due to the presence of algae in the water. With our Florida sun and warm climate, this helps algae grow at a rapid rate - which explains why some pools can suddenly become green overnight.

But the main reason for pools turning green is lack of or little chlorine or chemical imbalance of our pool water. Chlorine is one of the most common and effective sanitizers, but unfortunately, its efficiency highly depends on the water chemistry. When chlorine levels drop, even for just a day, algae will already start evolving in your pool water.

Is it Dangerous to Swim in a Green Pool?

Generally, it is not dangerous to swim in a green pool. Most people will prefer not to swim in it because it’s annoying to feel the algae all over your body as they swim. But if it’s not treated for a long time, the pool water will be infected with harmful bacteria such as e-coli. So make sure that the pool is at the right chlorine level before swimming in it.

How to Fix a Green Pool

You might be thinking that you have to drain your pool, but don’t worry, that’s not the first step of fixing a green pool. I know how tedious it is to drain a pool so I’m glad to share with you that we can return our pool to its normal state with other methods.

Determine the Severity of the Algae Infestation

Good news, if your pool has a lighter green color, then it means that the algae are just starting to spread. If it has a darker green color, you will still be able to handle clearing your green pool without changing the water. 

But when you’re faced with a really dark shade of green, you’ll have to drain your pool or hire a professional. Here’s an example of a dark green pool that a professional had to drain and clean the walls and floor.

If your pool is not this dark, you can try the other methods.

Shock your Pool

One of the fastest ways to clean green pools is to shock your pool, which is boosting the chlorine level and maintaining it at that level until the algae dissipate.

Here’s a video on how they were able to clear a green pool that has been neglected for four years. We can also apply the same method for cleaning our green pool.

Materials: Pool water test kit, pool shock 

Equipment: Net, brush, telescopic pole, vacuum

Step 1. Clear out the debris. Use the net to remove any floating leaves and the vacuum for debris that settled at the bottom of the pool.

Step 2. Test your pool water. 

pH Level: The pH levels should be between 7.5 to 7.8. If it’s below 7.5, use soda ash or pH increaser, but if it’s above 7.8, use muriatic acid or pH decreaser.

CYA level: The CYA level of non-saltwater pools should be between 30 to 60 parts per million, while a saltwater pool should have 70 to 80 parts per million. To fix the CYA levels, use this calculator to determine how much cyanuric acid you will need to add or remove (you can only reduce the CYA level by removing water and adding freshwater).

Free Chlorine Level: Read the high chlorine level so you can continue to the next step.

Step 3. Determine the shock level you will need to clean your pool based on this CYA/Chlorine chart. Use the calculator above to determine the exact amount.

Step 4. Once you have determined how much pool shock to apply, make sure that the pump is running continuously while shocking your pool. This will help properly circulate and filter your pool.

Step 5. Maintain the shock level of your pool to effectively clear the water. As algae are being removed, the chlorine level will go down as well. Check the Free Chlorine level every two hours and add the required chlorine to maintain the shock level.

Note: It will eventually reach a point that chlorine won’t deplete as fast since there are fewer algae in the pool.

Step 6. Clean your filter daily to remove the dead algae that the filtration system has captured. You will also need to brush the walls and vacuum the floor since algae have settled at the bottom.

Step 7. Your pool should start turning cloudy blue, but once it’s clear, you need to perform another test to see if there are any algae left. Check the Free Chlorine level in the evening and before the sun comes up. If the Combine Chlorine level is less than 0.5 parts per million and your Free Chlorine level didn’t drop or dropped less than 1 parts per million, then your pool is all set!

IF NOT, continue to maintain the shock level of your pool until the data matches the numbers above.

Use a Flocking Chemical and Algaecide

Another method you can use is pool flocking.

Time: 3 to 3.5 days

Materials: Algaecide, 2 bottles of pool flocking chemical

Equipment: Brush, telescopic pole, vacuum

Step 1. Add a bottle of algaecide and a bottle of pool flocking chemical to kill the algae, this will turn it white and make the pool cloudy. Check the manufacturer’s instructions for the amount you will use, but generally, a 10,000-gallon pool will need 8 ounces of pool flocking chemical.

Step 2. The flocking chemical will bind the particles suspended in the pool water and bring the white debris to the bottom. Wait for 24 to 36 hours after the first step since the process will depend on the amount of chemical and state of the green pool. 

Note: Your pool will clear up and you’ll see the bottom, probably not at the deep end and it will also still be cloudy.

Step 3. Once your pool has become blue again, add another bottle of pool flock chemical and brush the floor to stir up the white debris while letting the pump run for two hours. Place your pump on the ‘waste’ setting and then turn it on.

Step 4. Wait for another 24 hours. After, vacuum the pool to remove the leftover white and powdery algae.

What is Pool Flocking?

Pool Flocking is using a chemical that binds the floating debris in the water. This will cloud up the water, but it catches tiny particles that cannot be cleaned by the filtering system. Compared to pool shocking, flocking a pool is less expensive and has less effect on the pH levels.

Why is the Water Still Cloudy After Cleaning a Green Pool?

It’s normal for your pool water to be cloudy after cleaning your green pool. This is because dead algae turn into cloudy debris. Turn on your pump and filter to remove these white algae or you can use a pool clarifier to quicken the clearing process. The time will still depend on the size of your pool, the capability of your filtration system, and the severity of the algae infestation.

Reasons why your Pool Water is still Green after Treatment

Despite your efforts, your pool might still be green. Here are some reasons why it won’t clear up.

Water chemistry is not balanced: If your pool water chemistry is not balanced, then the chlorine won’t be effective against algae. Test your water and make sure it is balanced before the treatment.

Not enough chlorine: When shocking your pool to remove algae, it is important to use the right amount of chlorine. If you are following the manufacturer’s instructions or are not consistently monitoring your chlorine levels, then your pool will not become clear. The amount you use for regular pool shocking will not be enough to kill algae.

Don’t rely on just algaecide: Algaecide is not a solution but for prevention. This chemical alone will not clear your green pool or kill algae. It will be effective on its own once the water is clear again.

Run your filter: If you did everything right but failed to run your filter 24/7, then it won’t work. It’s important to constantly circulate the pool water when treating a green pool. You also have to constantly clean and check if your filter is working efficiently.

Wrong filter: Your filter is working, but if it’s not the right size for your pool, it can’t do the job. Check this guide to see what filter size is best for your pool. In the long run, the right filter will also help prevent algae from developing in your pool water.

5 Tips on How to Prevent your Pool from turning Green again

1. Check Your Water Chemistry Weekly

You will need to regularly test your pool water’s chemistry and balance it. You should always maintain the right level to prevent algae from developing in your pool. Use the chart to determine the right Free Chlorine level based on the current CYA level of your pool.

2. Maintain a Proper pH Level

You should also test your pH level and make sure they are between 7.4 to 7.6.

3. Brush and Vacuum

Another way to prevent algae from returning is to regularly clean your pool. Brush and vacuum the walls and floor of your pool to remove contaminants. If you don’t have the time, invest in an automatic pool vacuum.

4. Use Algaecide

Add an algaecide to your pool water every week, just to be sure. This is an effective prevention against algae, especially when the pool is already clean and clear. Remember, don’t just rely on algaecide or else you'll find yourself with a green pool again. You need to regularly clean your pool and follow the next step as well.

5. Clean your Filters

You can keep your pool clear and blue if you make sure that the filtration system is also clean and working. The filter must be the right size for your pool so it will be effective against algae and other contaminants.

Do I Try to Remove the Algae’s Food Source?

Phosphates, which are present in our pools, are the food source of algae. Logically, removing these will prevent algae from invading our pools - but in reality, it will not. Don’t spend on a phosphate remover since it would be impossible to completely remove the phosphates from your pool. Instead, use the money to regularly clean your pool.

Green Pool: Not Because of Algae, but Pool Shock

Pool shocking is part of maintaining your pool, but some people are surprised to see their pool turn green after this process. This can happen if there are metal particles in your pool water.

One of the main culprits is copper. The pool may turn green if there is too much dissolved copper present in the water. They can either naturally appear in your water or leech into your pool from the copper plumbing. 

Unlike an algae-caused green pool, you don’t have to follow a lot of steps to clear your pool. You will need a chelating agent to remove the copper present in the pool water. 

Note: Look for a chelating agent that is made for swimming pools,

To prevent this from happening again, test your water for copper levels regularly. Don’t forget to test your water before shocking, especially if you have copper plumbing.

Kenneth Wilson
October 21, 2019
Yard & Garden

Kenneth Wilson

Retired contractor. Currently residing in Southwest Florida. Now in semi-retirement, I write and manage this blog focused on helping home owners make savvy decisions when it comes to finding contractors and getting their projects done. I also operate remodeling design service for homeowners.

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