You walk outside expecting to enjoy a refreshing swim, only to discover your pool has turned an unpleasant shade of green.
If you've ever asked yourself, "Why is my pool green?", you're not alone. It's one of the most common questions we hear at Pool World Australia.
The good news is that a green pool is usually treatable—and the sooner you identify the cause, the easier it is to restore your pool to sparkling, crystal-clear water.
Let's look at the most common reasons your pool has turned green and what you can do about it.
The Most Common Cause: Algae
In most cases, a green pool is caused by algae.
Algae are microscopic organisms that thrive when your pool water isn't properly sanitised or balanced. Once algae begin to grow, they can spread quickly—especially during warm weather.
Common causes of algae growth include:
- Low chlorine levels
- Poor water circulation
- Infrequent pool maintenance
- Dirty filters
- Unbalanced water chemistry
- Heavy rain or storms
- Extended periods without running the pool equipment
The earlier you treat algae, the easier it is to remove.
Low Chlorine Levels
Chlorine is your pool's primary defence against bacteria and algae.
If chlorine levels fall too low, algae can begin to grow rapidly.
Low chlorine can be caused by:
- High pool usage
- Hot weather
- Heavy rainfall
- Strong sunlight
- An ageing salt chlorinator cell
- A chlorinator that's not producing enough chlorine
If your pool is green, checking the chlorine level should always be one of the first steps.
Low Chlorine Levels – Is Your Salt Cell Wearing Out?
One of the most common reasons a pool turns green is low chlorine levels.
For saltwater pools, this doesn't always mean you need to add more salt. In many cases, it could mean your salt chlorinator cell is no longer producing enough chlorine.
As salt cells age, their ability to convert salt into chlorine gradually declines. This can leave your pool vulnerable to algae growth, even if your pump is running and your salt level appears to be correct.
Signs Your Salt Cell May Need Replacing
If you're experiencing low chlorine levels, check for these common signs:
✔ Your salt cell is over 4 years old – Most salt cells have an average lifespan of 4–5 years, depending on usage, water balance and maintenance.
✔ The cell plates are uneven or heavily worn – Look inside the salt cell. If one or more of the plates are noticeably shorter, thinner or more corroded than the others, it's a strong indication the cell is reaching the end of its life.
✔ Your chlorinator is displaying a Low Salt warning, even though your pool has been professionally tested and the salt level is correct.
✔ You're needing to add chlorine more frequently to maintain safe sanitiser levels.
✔ Your pool starts turning green despite regular maintenance and the equipment appears to be operating normally.
Don't Assume You Need More Salt
A common mistake is adding extra salt as soon as a Low Salt warning appears.
However, a low salt warning can also be caused by:
- A worn-out salt cell
- Cold winter water temperatures
- Calcium build-up on the cell plates
- A faulty sensor or chlorinator
- Incorrect water chemistry
Adding salt without first testing your water can result in excessively high salt levels, which may contribute to corrosion of metal components and place unnecessary stress on your pool equipment.
The Best First Step
Before adding any chemicals or replacing equipment, bring a water sample into Pool World Australia.
Poor Water Balance
Even if your pool contains chlorine, it may not be working effectively if your water chemistry is out of balance.
Important water parameters include:
- pH
- Total Alkalinity
- Stabiliser (Cyanuric Acid)
- Calcium Hardness
- Salt level (for salt pools)
When these levels are outside the recommended range, chlorine becomes less effective, giving algae the opportunity to grow.
That's why professional water testing is so important.
Your Filter May Need Attention
Your filtration system removes dirt, debris and microscopic particles from the water.
If your filter isn't working efficiently, algae can multiply more easily.
Common filter issues include:
- Dirty cartridge filters
- Sand that needs replacing
- Blocked media filters
- Not backwashing often enough
- Damaged filter components
Regular filter maintenance is essential for keeping your pool healthy.
Is Your Pool Pump Running Long Enough?
During warmer months, your pool needs adequate circulation to distribute sanitiser throughout the water.
If your pump isn't running long enough, stagnant areas can develop where algae begin to grow.
Every pool is different, and the ideal running time depends on:
- Pool size
- Water temperature
- Bather load
- Type of sanitising system
Our team can help you determine the best running schedule for your pool.
Heavy Rain Can Trigger Green Water
Many pool owners notice their pool turns green after heavy rain.
Rainwater can:
- Dilute chlorine levels
- Wash debris into the pool
- Alter water chemistry
- Introduce contaminants
After significant rainfall, it's always a good idea to have your water professionally tested to ensure it remains balanced.
It Might Not Actually Be Algae
Although algae are the most common cause, green water isn't always caused by algae.
Other possibilities include:
Metals in the Water
High levels of metals such as copper or iron can cause water to develop a green or green-brown tint.
This is why it's important not to assume your pool simply needs more chlorine.
Professional water testing can identify whether metals are contributing to the problem.
Why You Shouldn't Guess with Pool Chemicals
One of the biggest mistakes pool owners make is adding chemicals without knowing what's actually wrong.
Adding unnecessary chemicals can:
- Waste money
- Delay the correct treatment
- Unbalance your water further
- Potentially damage pool surfaces or equipment
The best approach is to test the water first.
How Pool World Australia Can Help
If your pool has turned green, don't panic—we're here to help.
Simply bring a water sample into Pool World Australia, and we'll carry out a professional water analysis.
We'll explain your results in easy-to-understand terms and provide clear recommendations to help restore your pool quickly and safely.
If the problem is more severe, we also offer professional pool servicing and green pool recovery services.
How to Prevent a Green Pool
The best cure is prevention.
To reduce the risk of algae:
✔ Test your water regularly
✔ Keep your chlorine at the correct level
✔ Maintain balanced water chemistry
✔ Clean your filter as recommended
✔ Empty skimmer and pump baskets
✔ Brush and vacuum your pool regularly
✔ Run your pool equipment for the appropriate amount of time
✔ Bring a water sample into Pool World Australia for professional testing at least once a month
A little routine maintenance can save you time, money and frustration.
Don't Let a Green Pool Ruin Your Summer
A green pool doesn't have to stay green.
With the right advice, accurate water testing and the correct treatment, most pools can be restored to sparkling condition.
At Pool World Australia, we're passionate about helping Perth pool owners enjoy clean, healthy water all year round.
Whether you need professional water testing, pool chemicals, equipment advice or a complete green pool recovery, our friendly team is ready to help.
Visit our Balcatta showroom today and let's get your pool back to its best.
Frequently Asked Questions
Why did my pool suddenly turn green?
The most common cause is algae growth due to low chlorine levels or unbalanced water chemistry. Heavy rain, poor filtration or inadequate pump run times can also contribute.
Can I swim in a green pool?
It's best to avoid swimming in a green pool until the water has been tested and treated. Green water can indicate algae growth or other water quality issues that may affect swimmer comfort and hygiene.
Will adding more chlorine fix a green pool?
Not always. While chlorine is often part of the solution, simply adding more without testing the water may not solve the underlying problem. Professional water testing ensures the correct treatment is used.
How often should I have my pool water tested?
We recommend professional water testing at least once a month, and more frequently during summer, after heavy rain or if you notice changes in your pool water.
