Why Is My Pool Water Green? [And How To Fix It Fast]

Why Does Pool Water Turn Green
Written By: Chris Tebbutt
Date Published: February 27, 2019

Why Does Pool Water Turn Green and exactly what are the consequences of swimming in green pool water? Well, there are a lot of questions related to this, but first, let's go over why your pool is green in the first place.

What is known as algae make a pool green. While generally, algae are harmless in a river, in a pool it is a different story. In a pool, it mostly looks dark or light green and cloudy. Adding chemicals can prevent the water from turning green, as it lowers the ph level, which kills algae.

Why Does Pool Water Turn Green?

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There may be a few reasons why your formerly clean pool water turned green. These reasons include chemical imbalance, poor circulation, faulty cartridge filter, and not enough chlorine in the pool. However, the main cause is algae. Pool water turns green when green algae grow on the pool's surfaces. Algae is a plant-like organism that contains chlorophyll, which allows it to photosynthesize and produce its own food. When conditions are right for growth, algae can reproduce quickly, resulting in a green swimming pool.

While algae are not harmful to humans, they can make swimming uncomfortable and attract other hosts of bacteria, bugs, and animals. In addition, who wants to swim through the muck and nasty dark green water while going for a refreshing dip?

Preventing Green Water in Swimming Pools

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As a pool owner, if you notice the color green in your pool water, then your best bet is to rely on chemical treatments to kill algae. Chlorine and chlorine shock should be used in regulated amounts to lower the high ph and maintain the chemical balance of the water. Too high chlorine levels leads to excess of metal components and cloudy water, while too low chlorine levels can’t control the algae and completely clear the water. Additionally, to properly treat the water, you should examine your pool filters. For a diatomaceous earth filter, consider using phosphate remover, granular shock, and liquid chlorine to chemically clean all the algae. Keep in mind that the ideal time for pool cleaning is during night, as the sun is the food source for algae and leads to excessive growth of it, known as algae bloom. Moreover, chlorine tends to lose its effects under sunlight, which is why cyanuric acid is recommended. Carefully observe the chemical levels of the cloudy water to control algae and to achieve a beautiful clear pool.

To sum up, there are a few things that you can do to help prevent algae growth in your swimming pool. Regularly running your pump and cleaning your filter is a must, but some other things you should do are:

  • Make sure that you are properly chlorinating the water. Pool algae thrive in warm, moist environments, so it's important to keep the water as clean and free of debris as possible.
  • Brush the pool walls and floor of the pool regularly to remove any algae that might be starting to grow.
  • Pool shock on a regular basis kills any green algae spores that might be present in the water.

Overall, there are a number of things that can contribute to pool algae and algae blooms, which include sunlight, warm temperatures, and high levels of nutrients. By keeping your pool clean and balanced, you can help to prevent algae from taking over.

In a lot of cases, people continue using the pool without realizing a broken filter or pool pump, so regularly checking on your equipment is advised.

How To Clean Green Pool Water

What Does Pool Service Include

If your pool is green, depending on the severity, there are a few measures you can take to get rid of algae. In some cases, it may take only a day or so, whereas it may take more than a week to clean everything up in other cases.

In severe cases, you may even need to consult a local pool cleaning company.

Total Time: 7 days

Inspect the green pool

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Depending on the severity of the algae in your pool, you may have to drain the pool water, but in most cases, you probably don't have to.

If the water is more or less clear and you can see the bottom of your pool, you don't have to drain it. However, if you can't see more than 5-7 inches into the pool water, then maybe consider draining, but plenty of people are able to kill off algae without draining the water.

Cleaning your green pool

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Remove any debris, and leaves, and scrub the pool floor or walls to remove any pool algae and any other junk. You can use a pool vacuum or if you ended up draining the pool water, you can sweep everything.

Also, be sure to clean your pool basket + pool filter, and check whether the pump, filter, and other pool equipment are working as intended.

Adjust PH and alkalinity levels

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Get one of these test strips from Easy Strips and check your pool PH and alkaline levels.

You want the water PH levels not to be much more than 7.5 and the alkalinity level no more than 150 ppm.

You can use something like PH/alkalinity reducer to get it to your desired levels. Before you use pool shock and other pool chemicals, it's recommended to get PH and alkalinity levels balanced otherwise the water will get cloudy and murky.

Pool shock with chlorine

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Because algae grow during the day, it's better to use shock treatment during the night.

Use something like HTH Pool Care Shock for this. It's compatible with pretty much all kinds of pools and does a great job at killing algae in your pool.

You want 4X the chlorine than usual in order to shock the pool, but with HTH Pool Care, for a 10000-gallon-size pool, around 1.5 pounds should be enough. Do this for a few days until the pool green disappears.

Some pool owners say not to run the pump until the water color changes from green back to usual, but others will argue to run the pool's filter during the shock process. I would say as long as you regularly clean your cartridges/backwash your filtration system, you should be good.

The pump helps circulate the chlorine and other chemicals around the pool instead of concentrating on one area.

Run your pool filter until all is clear

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After all the shock, the pool will become more of a cloudy blue.

Sometimes you will also have patches of dead algae and organic matter on the bottom floor. Use a pool vacuum to clean them.

You will need to run the pump and filter until the pool water is visible and clean. You may have to run the pump longer than the usual 8-hour recommendation for a few days in order to get rid of the cloudiness.

If you suspect there is still some algae, shock your pool until you don't see any hint of pool algae. Lastly, make sure to check your filter and backwash/clean more frequently during this process.


  • Algecide
  • Clarifier
  • Shock
  • Pool Salt
  • Other Chemiacals


  • Scub
  • Gloves
  • Safety Glasses
  • Pool Vacuum

Frequently Asked Questions

Here are some other important things you should know when dealing with a green pool and getting rid of pool algae.

Is swimming in green pool water dangerous?

When your pool has lots of algae, your FC (free chlorine) level is nearly 0. Without any FC, generally speaking, a pool is unsafe to swim in. It's not exactly the algae that are dangerous to health, it's actually the other things that end up in the water.

Without FC, and with all that algae, what ends up happening is certain bacteria have the potential to thrive.

So while you might not mind the Algae, you may mind the fresh duck fecal matter that has been sitting on top of the water for the past week! While you are not guaranteed to get sick from swimming in a pool with algae, it really isn't a good idea. I mean you wouldn't swim in a swap, would you?

Why can I swim in a lake but not in green pool water?

Lakes and rivers do get algae, but they are more of a self-sustaining ecosystem.

Lakes have a fine balance of bacteria, much greater water volumes, and filtration going on by the plant life.

However, there are issues with bacteria in lakes too, many beaches will shut down on really hot days if the bacteria is off the charts, but harmful bacteria are more likely to thrive in a small space of a pool.

Closing Thoughts

So if you don't want to deal with the mess and prevent green pool water, you need to spend time on pool maintenance, backwash/clean your filter, and check your equipment for anything that may not be working. It's necessary if you don't your pool water to turn green.

If you do end up with a green pool and pool algae, you need to shock the water with chlorine and something like HTH Pool Care as per the instructions above.

If all else fails, you may need to call professional pool cleaners, but in most cases you should be fine.

Article written by Chris Tebbutt
In 2016 I got my first house that had a pool and I had no idea where to begin. Over time I have learnt how to do most things myself (I am really into DIY) and wanted to share my information with other. I was one of the people who thought if water smelt like chlorine, that meant there was too much chlorine in the water!