POOL & WATER MAINTENANCE

How to Clean a Green Pool Water

Nothing ruins those summer vibes faster than realizing that your pool is green. Myriad factors can turn that crystal-clear water into a disappointing mess. Fortunately, help is at hand.

On this page, we’ll run you through how to fix cloudy green pool water, proper pool maintenance, cleaning, and much more.

Why do swimming pools turn green?

When your pool is green, what caused the change? The frustrating news here is that there are myriad factors that can cause algae and other contaminants to enter your pool. In this section, we’ll explore the main causes.

In A Nutshell – Why do Swimming Pools Turn Green
In short, the following usually cause swimming pools to lose their luster:

  • Pool filtration
  • Not enough chlorine
  • Excess chlorine (usually cloudiness)
  • High pH levels
  • Too much CYA (cyanuric acid)
  • Rampant algae growth (made possible by the chemical imbalances above)
  • Excess pollen
  • Levels of metals like copper

Green Algae in Pool

For the most part, the green ‘sludge’ / material you’re seeing in your pool is caused by algae. So, when you ask why your pool’s green, you may as well be asking ‘what allows algae to grow?’ The answer here is usually a chemical imbalance and/or a dirty filter.

Darker green spots are a sign of a more mature infestation. Light green pool water usually indicates that the algae has only recently taken hold.
When it comes to cloudy water, you’re dealing with a similar set of culprits. High CYA levels and poor filtration are common causes here.

Pool Turned Green Overnight

The cause here is often still algae, even if your pool turned green overnight. In warmer summer months, algae can spread remarkably quickly. If your chlorine or other chemicals are out of balance, it can be easy for the organism to take hold.

Pool Green After Rain

Pool chemistry is a delicate process – getting the balance right is vital. If it’s rained heavily overnight and your pool wasn’t covered, the concentration of things like chlorine in your pool will be significantly diluted, allowing organisms like algae to grow.

Is it Safe to Swim When Pool Water is Green?

Outside of running chemical analysis on your specific pool, the only honest answer to this question is ‘it depends.’ Algae itself isn’t inherently dangerous for humans. However, it can attract a plethora of bacteria and other pathogens that can cause nasty infections if you’re not careful. In general, it’s best to clean your water if your pool is green.

Green to blue pool in 4 steps


Help, my pool is green! Fortunately, returning your water to its crystal-clear glory isn’t rocket science. Check out our green to blue pool guide below.

1 – Clean the Pool Interior

Your first port of call should be to clean your pool’s interior. Removing debris and dirt from your pool’s surfaces will improve its appearance, reduce bacteria levels, and disrupt existing algae colonies.

In smaller pools, a brush and net may be enough for this job. Otherwise, a pool vacuum is probably necessary in your pool equipment .

You will need:

  • A vacuum head
  • A pool brush – this helps lift up more challenging debris
  • A vacuum hose (buy one that’s long enough for your pool – measure if unsure)
  • A vacuum handle (telescoping designs give better reach)
  • A skim-vac (lets you avoid using your strainer basket and instead filter things directly)

Once you’ve attached your vacuum to your filter, thoroughly clean every surface, nook, and cranny of your pool.

A Note on Robot Vacuums
It’s worth mentioning here that pool vacuums can save you a ton of time in this regard. Not only can they help clean your pool for you, but they also help prevent significant dirt built-up if you schedule them to clean regularly.

2 – Shock the Water

Wondering how to clean a green pool in 24 hours? A decent shock is sometimes the answer.

Once you’ve removed the majority of the ‘physical’ contaminants in your pool, it’s time to tackle the water itself. Shocking the water is sometimes enough to return your pool to its former state. Keep in mind, however, that you’ll also need to address the underlying issues that caused your green pool water in the first place.

So, what is a pool shock? Shocking your pool increases its levels of free chlorine and therefore helps to eliminate any live organisms that were causing that light green pool water or darker sludge spots. It’s a short-term ‘bomb’ that helps return your water to normal quite quickly.

In some cases, this chlorine injection is enough. Usually, however, it’s a good idea to test your pool’s chemistry and adjust your levels for a long-lasting clean.

Pool Still Green After Shock?

Pool still green after shock? There are a few things you might like to check. While a pool shock can be a great short-term solution, it’s not always enough to put things right. Your green pool water is probably being caused by some of the following:

  • There are metals like copper in the water that have oxidized
  • Your pH levels are wrong – See our guidance on chemistry
  • Your water is full of phosphates
  • There are still dead algae in your pool – robots and regular vacuums can help with this.

3 – Test and Balance Pool Chemicals

While it can be a tedious job, testing and balancing your pool chemicals is the only way to get a clear picture of the state of your water. This will help you maintain your newly blue pool well into the future.

You’ll be able to test for the following:

  • Total Chlorine
  • Free Chlorine
  • pH levels
  • Bromine
  • Alkalinity
  • Total Hardness
  • Cyanuric Acid

At the very least, you’ll want to be testing for chlorine levels, pH/ alkalinity, and cyanuric acid.

The Pool is Green, but Chlorine is High – Why Detail Matters


If the pool is green but chlorine is too high, you’ll have to test your water to determine what’s gone wrong. Don’t worry – it’s usually just a case of balancing your water chemistry and running your freshly cleaned filter.

Getting as much detail as possible here is vital. For example, data about chlorine levels alone might not be enough to change your situation; you’ll also need to understand how much of that chlorine is free chlorine and how much cyanuric acid is left in the pool.

In short, chlorine doesn’t stay useful in your pool forever. Exposure to sunlight and time in general will reduce the levels of ‘useful’ chlorine in your pool. Cyanuric acid is a chemical that helps to extend the half-life of chlorine and keep it useful for longer.

Too much or too little of any of these compounds, and cloudy, green water can start to appear. Understanding the details will help you adjust accordingly.

How to Fix Chlorine Levels
Chlorine levels too low? Chlorinating tablets can help get you back on track. Pay attention to the volume of water in your pool and the instructions on the packaging.

Did your tests show that your chlorine is too high? Exposing your pool to sunlight for a few hours should help bring things back to normal.

How to Fix pH Levels
When fixing your pool’s pH levels, you’ll either be adding something to increase the alkalinity of the water or instead raising its acidity.

4 – Run Pool Pump and Clean Filter

When was the last time you cleaned your pool’s filter? Be honest! Remove, clean, and replace your filter following your manufacturer’s guidance. In some cases, you may be able to simply backwash the filter once or twice to remove any unwanted debris.

Other times, however, it’s necessary to replace the cartridge in your filter system for best results. If in doubt, it’s best to replace for best results.

Follow these basic steps when cleaning:

  1. Check your filter for unexpected obstructions
  2. Backwash your system once or twice
  3. Check again to see if everything is cleared
  4. Clean manually or replace your cartridge if necessary

Running your circulation system with a fresh filter install can help to clear up any unwanted cloudiness and will prevent the green pool water from returning.

How to Clean a Green Pool Without Chemicals


The unfortunate truth is that the most effective way to clean and maintain your pool is to use harsh chemicals that aren’t great for the planet. However, this doesn’t mean it’s not possible to keep things clean naturally.

Below, we list a few ways that people clean a green pool without chemicals:

  • Thorough and regular vacuuming with a modified pool vac
    • A microfiber layer or a ton of cotton balls can be added to the mesh bag of your vacuum
    • This helps the vacuum pick up algae and prevent it from taking hold in your pool.
  • High salinity in the pool water
    • This cleans the water through electrolysis
    • Salt chlorine generators can help here
  • A phosphate removal treatment
    • Algae feed on phosphates in your pool’s water. Special treatments are available that remove phosphates from your pool altogether and therefore prevent any algae from feeding or growing.

    How to Keep Pool Algae from Returning

    So, you’ve learned how to clean a green pool fast. Question is, how do you keep that algae from returning? Below, we outline a few tips to help keep your pool crystal clear for longer.

    Rely on a Robot Cleaner

    Robotic pool cleaners can help transform your approach to pool maintenance. Their regular cleaning schedules and intelligent features are designed to keep your pool’s water in an optimum condition.

    The idea is to prevent algae from taking hold in the first place.

    Test and Tweak Your Chemistry Regularly

    It’s not enough to test your chemical balances once you spot green water. For best results, you should be running tests and tweaking accordingly at least once a month or so.

    Clean Your Filter Regularly

    Your pool’s filtration system is one of its best defenses against green, cloudy water. Make sure your cartridge and circulation system are all in good working order. Check at least once a month.

    Maintenance Chemicals

    Regularly adding maintenance chemicals to your pool can help to keep things looking crystal clear. They’re designed to balance elements such as pH, chlorine, and water hardness.

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