6+ Reasons Why Pool Water Turns Green

Green pool water can be due to high pH levels, inadequate chlorine, excess cyanuric acid, metals, high phosphate levels, or an ineffective filter.

why pool water turns green

Taking a dip in the swimming pool on a hot day is one of the best parts of Summer. Unfortunately, a pool filled with green water can be unsightly and even dangerous.

Green water is a familiar problem pool owners deal with every season. The first step to combating green pool water is to determine what is causing the discolored water. Below, let’s look at the top six reasons why your pool water is green.  

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High pH Levels

Keeping a safe swimming environment is all about the proper chemical balance. The pool water can appear green when your pH levels are too high.

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When the pH gets too high, it renders the added chlorine useless. Adding more chlorine will be ineffective if your pH is out of balance. It’s a good idea to aim for a pH level below 8.0. 

An ideal range for pH, where chlorine is most effective, is between 7.2 and 7.8. Remember that saltwater pools with chlorinators tend to have higher pH than traditional pools.  

Too Much or Too Little Cyanuric Acid

An excess of cyanuric acid is usually more of a concern for people who use stabilized pool chlorine or chlorine pucks in their pool. These tend to release cyanuric acid as a byproduct, leading to varying acid levels.

If the cyanuric acid is too high, it will prevent the chlorine from working to kill algae. If the level is too low, the chlorine ends up burning off the water’s surface too quickly by sunlight before it has a chance to kill algae.

It’s important to continually test your cyanuric acid level to ensure you are in the correct range. You want your pool water to be between 60 and 80 ppm.  

Low Chlorine Levels

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Chlorine is necessary for pool water because it helps clear and clean your water. The CDC recommends that free chlorine, abbreviated FC, should be between 1 ppm and 3 ppm to keep your water safe.

Follow the product label for accurate dosing, or use online calculators to dose your chlorine properly.

If your chlorine levels drop too low, you’ll lack any ability to fight off and prevent algae from spreading. You end up with green pool water when algae is free to spread.  

High Phosphate

If your chlorine, acid, and pH levels are all in the right range, there’s a chance you may have too many phosphates in your water.

Testing for phosphates can be tricky since the test is not usually included in universal pool test kits.

If you have already tried to balance pH, chlorine, and cyanuric acid without clearing up the green water, it may be time to suspect phosphates are causing your problem.  

Phosphates are naturally occurring and are jet fuel for algae. Fast-growing algae quickly consume phosphates, causing their populations to explode. Phosphates form from organic matter like leaves, grass, and bugs decaying in your water.  


Your green pool water may not be related to algae but instead connected to the presence of metal in your water. This reason for green water is more common in new pools that were recently filled.

Many water sources, especially well water, have a slight trace of metals. Cadmium, lead, copper, mercury, and arsenic are commonly found in well water.  

If you see green water form in your pool, chances are your immediate response is to add chlorine, thinking the green water is the result of algae.

Unfortunately, adding chlorine can only make the green water worse if your cause is trace metals. Additional chlorine can cause the metals to oxidize, turning the water a different shade of green.

The best way to combat metals in your pool water is to add a sequestering agent to the water. While the sequestrant won’t eliminate the metals, it will prevent them from leaching into the water, turning it green.

Usually, metals present in the water don’t pose a threat to your health but will make your water appear unsightly.  

Ineffective Filter

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Your pool’s filter works to pull out the pollutants from the water. Large detritus, like sticks and leaves, end up in the filter, and tiny microbes that are responsible for algae growth.

When you change your filter, you probably notice it’s mostly green. The green color is caused by trapped pollutants and algae that would otherwise live and spread in your pool water.

If your pool water is green, but your chemical levels seem correct, you may have an issue with ineffective filtration.

Try to change the filter pad more often or use a more robust filtration system. You may also want to increase the duration you run your filter.

Keeping your filter running for eight hours a day may be fine for normal pool usage, but if you have several people swimming, you may want to increase your filtration time to 12 hours or more.  

FAQs about Why Pool Water Turns Green

Can Too Much Chlorine Make Your Water Green?

While chlorine can help clear up green pool water, you can add too much of a good thing. Extremely high levels of chlorine can cause the metals in the pool and water to oxidize. When the metals oxidize in the water, the water will turn a different shade of green.  

How Do You Clear Up Green Pool Water Fast?

The best way to clear up pool water quickly is to start a two-part approach. First, you’ll want to shock your pool water at night.

High concentrations of at least 70% chlorine will help kill the algae. At night, algae doesn’t have the sun to grow and spread more, so chlorine is more effective.  

Secondly, you’ll want to continuously run your pool filter. Keep the filter running for 24 hours if possible.

As the chlorine starts to kill algae, you’ll have plenty of nitrate-producing detritus in your pool. Filtering this organic material out of the water will only help clear your water faster.  

Is it Safe to Swim When Pool Water is Green?

Swimming in green pool water can be safe, depending on the source of your green water. If your green water is caused by pollen in the area, it’s perfectly safe to swim, provided you don’t suffer from pollen allergies.

If your green pool water results from an algae bloom swim with caution. Several bacteria and toxins can feed on the blooming algae, which can enter the human body.

Microbes will likely enter the eyes, nose, mouth, or a tiny cut. Typically, the darker the green water is, the more algae there is. When there is more algae, you risk getting a parasite or bacterial infection.  

Why Does a Pool Turn Green Overnight?

Green water in your swimming pool is usually the result of algae. This aquatic plant is extremely fast-growing and can develop overnight in the right conditions.

Algae can bloom rapidly in warm conditions. If you notice your outdoor temperature is extremely hot, a pool with low chlorine levels may be a victim of an unfortunate rapid algae bloom.  

Where Should I Start to Clear Green Water?

Nobody wants green water in their swimming pool, so now you need to take the proper steps to remedy your algae issue.

Taking the first steps to clear your pool water is easy and will lead to cleaner water. To start clearing green water, you should:

  • Vacuum visible waste
  • Use an algae brush after vacuuming
  • Chemistry test
  • Shock the pool with concentrated chlorine

For a long term solution, you can also consider a screened-in pool, regular testing, and more frequent maintenance.

More FAQs

What is the best way to treat a green pool?

The best way to treat a green pool is to start by testing and balancing the water. After that, it is important to clean the pool water and surfaces by skimming the surface, brushing the walls, vacuuming, and emptying skimmer baskets. Next, apply a shock treatment and an algaecide to effectively eliminate any algae. Lastly, make sure to clean the filter to maintain proper filtration.

How do I get my green pool blue again?

To transform the question into a statement: “You can get your green pool blue again by following these steps:”Rephrased answer: “Start by removing leaves and debris from the pool, then proceed to clean the pump and filter. Next, vacuum the pool thoroughly. After that, add chlorine to the water to help eliminate algae. Additionally, make sure to scoop out any remaining debris and continue vacuuming as needed. Finally, establish a regular maintenance routine to keep your pool blue and clean.”

What turns a pool green overnight?

A pool can turn green overnight due to the rapid growth of algae, which is particularly likely to occur in warmer temperatures, especially if it is very warm outside.

Will baking soda help clear a green pool?

Baking soda does not kill algae in pools, as only algaecides have that capability. However, it can assist in clearing up algae. By using both baking soda and algaecides, you can effectively restore the water to a sparkling and clean condition.

What is a homemade remedy for green pool?

A homemade remedy for a green pool is to use household borax, which can be used as a spot treatment for blue and green algae, similar to how baking soda is used for black algae. By scrubbing the pool walls with borax and using a brush to dislodge the algae, you can effectively remove it. Afterwards, you can either vacuum or scoop out any remaining free-floating algae.

What kills green algae in a pool?

Green algae in a pool can be killed by shocking the pool. Shocking involves adding chemicals to the pool to increase chlorine levels and eliminate bacteria and algae. To effectively treat algae issues, it is advisable to use a calcium hypochlorite shock.

Can you fix a green pool without draining?

The question is: “Can you fix a green pool without draining?”Rephrased answer: It is possible to fix a green pool without draining if you can still see the shallow end floor, even if it’s barely visible. This can be achieved through extensive use of chemicals, thorough cleaning, and effective filtering. However, if the visibility is limited to only 12-18” and there is a significant amount of debris in the pool, attempting to restore it without at least partially draining will be a challenging and time-consuming process.

Can too much chlorine make pool green?

Too much chlorine can cause pool water to turn green due to the oxidation of metals like copper present in the water.

How do I stop my pool from turning green?

To stop your pool from turning green, you should regularly test and balance the water. It is crucial to pay close attention to the Free Chlorine level, as low levels can lead to green pool water. Make sure to maintain Free Chlorine levels between 1 – 4 ppm. If necessary, apply the necessary chlorine and sanitizers to restore proper sanitizer levels.

How long does chlorine take to clear green water?

The time it takes for chlorine to clear green water can vary, but typically it may take around 3 to 4 days. To effectively kill algae, it is important to raise the chlorine level in the pool by shocking it and maintain that high level until all the algae is eliminated. This can be achieved by using chlorine or other sanitizing products, as well as copper-based algaecides available in the market.

Does pool algae like high or low pH?

Pool algae tends to thrive in environments with higher pH levels, typically ranging from 8.2 to 8.7.

Is it OK to swim in a green pool?

It is not advisable to swim in a green pool, even if you are eager to cool off. If your pool water has turned green due to the presence of algae, it is recommended that you think twice before jumping in. Algae growth promotes the development of bacteria such as E. Coli. Opting to swim in a pool with algae exposes you to the risk of acquiring a rash, infection, or illness.

Will chlorine fix a green pool?

Chlorine can effectively clear up a green pool. Sufficient amounts of chlorine are able to eliminate the algae responsible for causing green pool water. However, it is important to note that a significant quantity of calcium hypochlorite super shock is required for this purpose.

Can a green pool be saved?

A green pool can be saved by following these steps: Boost your chlorine levels with a shock treatment and supplement it with an algaecide like BioGuard Burn Out Extreme and BioGuard Algi Destroyer for the most effective and fastest results.

How do I fix my green pool?

To fix a green pool, start by testing and balancing the water. Next, clean the pool water and surfaces by skimming the surface, brushing the walls, vacuuming, and emptying skimmer baskets. Then, apply a shock treatment and an algaecide. Lastly, clean the filter.

How long does green water take to clear in a pool?

The green water in a pool typically takes around 3 to 4 days to clear by shocking the pool with chlorine daily. Additionally, running the filter continuously for 24 hours a day and backwashing daily can help clear the green and any resulting cloudiness, which usually takes up to 7 days, but sometimes may take as long as 2 weeks depending on the filter.

Will green algae in a pool hurt you?

Green algae in a pool can potentially harm you due to the bacteria that thrive on them. While the algae itself may not be harmful, the presence of bacteria can pose a health risk to humans. Exposure to green algae can result in bacterial exposure, which may cause skin rashes and various skin irritations.

Can you get in a pool with algae to clean it?

It is possible to get in a pool with algae to clean it, but it is important to be aware of the potential health risks. The bacteria feeding on the algae can be harmful and may lead to skin infections. While the common green algae itself is not harmful, exposing yourself to algae that harbor bacteria can result in rashes and breaks in the skin.

Does algaecide really work?

Algaecide does work to some extent, although the exact mechanism behind its effectiveness remains uncertain. It is worth mentioning that if you reside in a region with elevated levels of metals and have filled your pool with such water, there is a potential risk of oxidation that can lead to staining of your pool.

Why is my pool still green after shocking?

If your pool is still green after shocking, it is possible that the green hue in the water was not completely eliminated. This could indicate that algae were not the cause initially, or that your cleaning procedure may not have been sufficiently thorough.

Can you put too much shock in a green pool?

It is possible to put too much shock in a green pool, although it would require a significant amount to render the water unsafe for swimming. To ensure a safe swimming environment, it is recommended to regularly test the pool water and maintain free chlorine levels between 1-4ppm.

How do I get my pool from green to blue?

To transform the question into a statement, it would be: “You can get your pool from green to blue by following these steps.” Rephrased answer: Start by brushing the walls and floor of your pool. Then, test the alkalinity and pH level to ensure they are balanced. Next, shock your pool with chlorine to eliminate any algae. Run your pool filter for 8 hours, and if necessary, shock the pool again. Finally, continue testing the water and adjusting the pool chemicals as needed.

Does high alkalinity cause green water?

High alkalinity can cause green water in your pool. The reason your pool water is green is due to an imbalance in pH, which renders your chlorine ineffective. Consequently, your filtering system is not functioning properly. The presence of algae is the primary cause of the green color, and this algae growth is directly linked to an imbalance in pH and/or alkalinity, even when there is sufficient chlorine.

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