July 31, 2023
min read
Maintenance & Care

The ultimate guide to fixing a green swimming pool

Having a dark green pool is not only unsightly, but it can also be dangerous. Not only is the water unsafe to swim in, but it can also be a breeding ground for mosquitoes.This blog post will discuss the causes of green pools and how to fix them. We will also provide tips on preventing your pool from turning green and killing algae in the first place. Let's get started.

Rhiannon Royall
The ultimate guide to fixing a green swimming pool

What causes pool water to turn green?

A green pool is usually the result of an algae bloom. Algae are single-celled organisms that thrive in warm, moist environments. They can reproduce quickly when conditions are right, leading to a green pool. Several things can cause algae blooms, including:

1. Algae

Pools are often green because of algae growth or an algae outbreak. Algae is a plant-like organism that grows in water and produces oxygen through photosynthesis. While algae are not necessarily harmful, they can cause problems in pools, including discolouration and odour.

Several things can contribute to algae growth in pool water, including sunlight, warm water, and high levels of nutrients.

2. Minerals and metals

Another possible cause is the presence of minerals and metals. This can often happen if the pool water has been sitting for an extended time, as these substances can build up over time. Minerals and metals can include copper, iron, and calcium.

3. Bacteria

Bacteria can also cause green pools. This is often the case with swimming pools that are not properly maintained and have not been adequately cleaned or chlorinated. Bacterial growth can lead to green or cloudy water and an unpleasant odour.

5. pH levels

An imbalance in pH levels can also cause green pools. According to SPASA (Australian Swimming Pool and Spa Association), the ideal pool water pH level is between 7.2 and 7.8, so if the water is too acidic or alkaline, it can lead to green discolouration.

An acidic swimming pool has a pH level of less than 7.2, whereas an alkaline pool has a pH level greater than 7.8.

Acidic water can be caused by rainwater and other contaminants entering the pool, while the overuse of chlorine or other pool chemicals can cause too much alkalinity.

6. Improper chlorine levels

The chlorine levels in your pool prevent it from turning green. If the chlorine level is too low, algae can grow and multiply. If chlorine is too high, it can cause skin irritation and other health problems. Proper chlorine levels should be between 1.5 and 3 ppm.

7. Inadequate circulation

Inadequate circulation is one of the most common causes of pool algae growth. If your pool doesn't have enough circulation, the water will become stagnant and unable to filter the chlorine properly. This will cause the chlorine to break down, and the water will become green.

8. Debris in the water

Debris, such as leaves and other organic floating matter, can cause green pools. This is because the waste will decompose in the water and release nutrients that can feed algae growth. This debris can also sink into the pool floor if not removed.

9. Improper pool maintenance

Finally, improper pool maintenance can also start an algae outbreak. This includes not cleaning the pool floor, wall, and the surrounding area or changing the water regularly. Testing the water and adjusting the pH levels as needed is also essential.

10. Sun exposure

Harmful UV rays from the sun can also cause green pools. The UV rays will break down the chemicals used to keep your pool clean and healthy, allowing algae to grow and spread.

How to fix a green pool?

1. Check pH levels

The pH level is one of the first things you should check if your pool is turning green. If the pH levels are too high or too low, it can cause algae to grow. You can check the pH levels with a pool pH testing kit.

You will need to adjust if they are not in the correct range. Maintain a pH between 7 and 7.6 to avoid any health risks.

A water pH above eight can cause skin rashes, while a pH below seven can sting the eyes.

2. Clean the pool

Cleaning your green pool is essential to get rid of any algae floating or debris that may be contributing to discolouration. Use a brush, vacuum, and skimmer to remove any stubborn dirt or debris from the pool walls and floors. Then use a chlorine shock treatment to kill any remaining algae.

3. Chlorine shock treatment

A chlorine shock treatment is a strong dose of chlorine to kill off any remaining dead algae or bacteria in the green pool. It would be best if you used it after cleaning the pool.

Make sure to follow the instructions on the package carefully and use protective gear when handling chemicals. Check chlorine levels frequently.

4. Clean the pool filter

If your pool's filtration system is not clean, it can also lead to algae growth. Make sure to clean your filter regularly and replace the filter media when needed.

Professionals suggest cleaning your cartridge filters every three months to avoid green pool water.

Filter replacement is between one and four years, depending on the type of filtration system. Do regular checks to see if your filter is performing optimally.

5. Increase circulation

If your green pool is caused by poor circulation, increasing the circulation can help improve the clarity of the water and prevent pool algae buildup. Adding a pump or adjusting equipment increases the speed and pool water flow.

Additionally, you can check that all the skimmers and drains are clear of any dead algae or debris.

6. Balance pool chemicals

It is essential to balance pool water chemicals regularly. If the chemicals are not in balance, it can create an environment where algae can thrive. You can use a swimming pool chemical kit to test and adjust chlorine, pH, and alkalinity levels. Swimming pool chemical kits are available at any local pool store and can cost between $10 and $30.

7. Add algaecide

If you have an algae problem, you can treat it with an algaecide. Many algaecides are available, so choose one compatible with your pool's chemistry. There are three types of algaecide:

  • Quaternary - for light green algae and mustard algae.
  • Copper-based for dark green and black algae.
  • Polyquat - for green and some types of pink algae.

These chemicals disrupt energy transport, cell division, or cell membranes, making the algae more vulnerable to sanitisers such as chlorine. Each type of algaecide differs in how effective it is and how much algae it can kill. Read the instructions carefully to ensure you use the algaecide correctly and in the appropriate dosage.

Tips to prevent a green pool

1. Keep the pool clean and free of debris

One of the best ways to prevent algae growth is to keep your pool clean and debris-free. Make sure to skim leaves and other debris from the water's surface regularly and vacuum the bottom of the pool at least once a week.

2. Test the water regularly

To prevent algae pools in the future, test the water regularly and adjust any levels (pH, chlorine, etc.) as needed. Professionals recommend trying your pool at least twice weekly to ensure it is safe and clean.

3. Use a pool cover

One of the best ways to prevent algae pools is to use a pool cover. Pool covers stop leaves and other debris from getting into the water, which can lead to algae growth.

They also help keep the water temperature consistent, especially during hot weather, which can slow down algae growth. The best pool cover materials are vinyl and solid.

4. Check your filter regularly

Make sure to check your cartridge filter periodically and clean it when needed. A dirty or clogged filter can reduce circulation, leading to green pool water. Always check if your filters are completely clear of any gunk.

5. Stay on top of maintenance

Regularly cleaning your pool, removing debris, and maintaining proper chemical levels will help keep green pools at bay. Following these steps can help ensure that your pool is clean and safe for swimming in no time. If you still have trouble getting the green out of your pool, it might be time to call in a professional. They can help diagnose the underlying cause of your green pool and suggest the best way to fix it


Following our guide, you can return your pool water to its original state in no time. Plus, we've also provided some tips on how to prevent your pool from turning green in the first place. If you need any further assistance, Poolz is here to help! We are the authority in connecting pool owners to pool businesses in Australia and would be more than happy to put you in touch with one of our trusted partners.

Keep your inground swimming pool looking perfect all year round by making sure you understand all the maintenance and care steps required.

Rhiannon Royall
Pool Builder Operations
I'm a pool enthusiast turned designer with 25 years of industry experience. Creating dream pools is my passion, and I'm thrilled to help builders and homeowners bring their visions to life through Poolz.
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