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Green Pool Cleaning - The Ultimate Guide

What to do When Your Pool is Green?

The colour green is oftentimes connected with promoting a calm mood. But a green pool will most definitely not help you feel calm at all. There are amazing emerald-coloured pools around the world, luring you with its deep green hue to dive in. Yet when it happens overnight to your pool, it means that you have a problem with an algae bloom.

It is not just aesthetically unpleasing, it can be a serious health hazard as well. Green algae often come accompanied by harmful bacteria feeding on them. Swimming in such waters increases the risk of skin rashes and various eye and ear diseases.

Before you start feeling blue, we will help you revert your pool back to its original state. Save these tips because they are evergreen (pun intended).


Why is My Pool Green?

In 99.9% of cases, a green pool means that you unfortunately have an active algae bloom. Green algae in the pool is a pretty common occurrence. The good news is that there is always a way to get it back to normal.

A green pool is most usually caused by:

  • Low free chlorine levels in pool
  • High temperatures
  • High humidity
  • Lots of recent rain
  • High phosphate levels in the pool
  • High pH levels

…often, it is everything from above. Heavy rains can dilute the chemicals in the pool, especially chlorine and salts, making this a perfect storm for green algae.


Common and Not So Common Green Pool Culprits

As mentioned above, in 99.9% of cases, a green pool means you have an active algae bloom. However what about the 0.1% of cases? Well, in swimming pools that are sanitised by copper (usually through an ionizer), sometimes a green pool can mean an excess of copper.

Ionized pools usually require an oxidizer to be added to the water to help remove the biological waste that the copper kills off, however, in RARE cases if the pool has too much copper in the water (above 0.6ppm) and/or too much oxidizer is added to the water, it makes the copper turn into copper oxide, AKA copper rust.

Copper rust is a bright green colour and will colour the water accordingly. Unfortunately, there is no effective way to fix this issue other than to lower the amount of copper in the water and to give the pool time to revert back to blue.


Green Algae in Pool Prevention

To prevent green pools, there are some steps you can take. Although it seems it happened overnight, there are certain signs you can’t miss. So prevention is always the best.

Steps for green pool prevention include:

  • Maintaining an appropriately high free chlorine level (ideally ~3ppm for Aus Summer) is one of the best ways to prevent a green pool as it will prevent algae from growing even under otherwise ideal conditions.
  • Checking the water balance.
  • Double-check if the water filtration system is working properly.
  • Shocking the pool once a week. If you apply shocking regularly, it will help you reduce cloudy waters which often indicate that algae growth is beginning. You can use chlorine-based chemicals like dichlor or calcium hypochlorite. It is important to mention that it must be done after you’ve applied algaecide. If you do this simultaneously, they can cancel each other out.
  • Algaecide should be used on a regular basis.
  • Clearing the filter, skimmer and pump regularly.
  • Vacuuming your pool.
  • Use a brush to clean walls, floor and steps. Your choice of the brush depends on the pool material. Don’t use wire brushes on acrylic, vinyl-lined, fibreglass and painted surfaces because you are risking serious damage. We highly recommend algae brush for a thorough cleanup.


Some Important Factors to Keep in Mind

However, a high pH level (above 7.6) will drastically reduce the effectiveness of your free chlorine, thus leaving it vulnerable to algae growth. Additionally, lots of rain and high temperatures can lower your pool's free chlorine level by diluting or evaporating the free chlorine respectively.

Additionally, rainwater will increase the number of nitrates and phosphates in your pool water, which promotes algae growth (think of it as extra food for algae). High temperatures and humidity are the ideal environments for algae growth and when following a large amount of rain creates a perfect storm for pool algae.


How to Fix a Green Pool: Green Pool Cleaning 101

The method you use to fix your green pool depends on how green the pool is, or how bad the algae bloom has become.

There are three broad green pool categories we encountered during our time in business.

The categories, in order of severity, are lightly green pool, fully green pool and swamp-like pool.


Steps to Take if the Water is Lightly Green

A lightly green pool is one where you’ve gotten on top of the algae bloom super quickly. This is usually characterised by maybe a faint tinge of green that has been there for less than 2 days. There will be very little or no algae sludge on the walls or floors.

Water should be clear or only lightly cloudy (can see the bottom). When your pool is only lightly green they’re very quick and easy to fix with the following steps:

  • Brush any algae gunk into the water.
  • Clean your filter (backwash & rinse for sand filters, hose out the cartridge for cartridge filters)
  • Add 15L of Liquid Chlorine per 50kL. Liquid chlorine is recommended because it starts working a lot faster, however, granular chlorine can be used if preferred. If you’re using granular chlorine, please consult the dosing rates of your specific granular chlorine and make sure to mix it up in a bucket of water 1st.
  • OPTIONAL: Add a clarifier tablet or floc block to the skimmer to speed up the water clarification process.
  • Run the pump for 24-72 hours straight as needed.
  • Get your water tested and rebalance the pool as necessary.


Fully Green Pool/Mustard Algae

A fully green pool is the next step after a lightly green pool. This is usually characterised by a very strong and definite green colour to the pool.

The pool can be anywhere from lightly cloudy to near opaque. There is usually the presence of algae sludge on the walls and floors.

Treating a fully green pool is a bit more involved and requires some more work as outlined in the following steps:

  • Get your pool water tested.
  • Vacuum as much algae gunk as possible out to waste (if possible). If there is A LOT of algae gunk, it is worthwhile trying to scoop as much out as possible before vacuuming.
  • Clean your filter.
  • From the water test in step 1, if needed, adjust your pool's pH level to less than 7.6.
  • OPTIONAL: Add a clarifier tablet or floc block to the skimmer to speed up the water clarification process.
  • Add 15L of Liquid Chlorine per 50kL. Advice about using liquid chlorine is the same as above
  • Brush as much algae gunk as possible to get it waterborne.
  • Run the pump for 7 hours to properly mix in the chlorine.
  • Add an appropriate amount of Algaecide (refer to dosing instructions of specific algaecide). A strong, copper-based algaecide is recommended. At DPS we recommend 1L of Hotzone Algaecide per 50kL.
  • Run the pump 24-72 hours straight as needed (until water is clear and blue).
  • Vacuum any residual dead algae gunk out to waste.
  • Get your water tested and rebalance the pool as necessary.

If the pool hasn’t become noticeably clearer after 72 hours, it’s recommended to add a strong clarifier to the water to assist the process.


Swamp Like Green Pools Cleaning

As the name implies, this is when a pool with an algae bloom has been left for an extended period of time and has become something more akin to a swamp than a swimming pool.

These pools are usually characterised by nearly opaque water, a significant amount of algae gunk and in extreme cases can be housing various creatures usually found in swamps.

Pools like this should be addressed as soon as possible, as they can be a health risk for the owner and their neighbours as they do attract a tonne of mosquitoes.

For the brave souls who wish to tackle the cleaning of a swamp-like pool by themselves, this is what I would recommend doing.

  • Make sure the pool is full of water.
  • Scoop as much of the algae gunk out as possible. This step can often be difficult due to limited water visibility but the more you can get out now, the easier your life is down the track.
  • Vacuum to waste as much algae gunk as possible. Difficult for the same reasons as step 2.
  • Clean your filters.
  • Add 10kg of strong Granular Chlorine (~700g per kg or stronger) to the water. Try and mix it up in a bucket of water 1st and walk it around the pool to spread it around faster.
  • Set your sand filter to recirculate or remove your filter cartridge and then run your pump for ~10 hours to mix in all the chlorine properly.
  • Scoop and vacuum to waste as much dead algae gunk as possible (again).
  • Using a strong granular floc, floc the pool.
  • Scoop & vacuum to waste any remaining algae gunk. Rinse and repeat until the pool is crystal clear.
  • Add an appropriate amount of Algaecide (refer to dosing instructions for specific algaecide). A strong, copper-based algaecide is recommended. At DPS we recommend 1L of Hotzone Algaecide per 50kL.
  • Get your water tested and rebalance the pool as necessary.


In Conclusion

You know just how frustrating green pools can be since it always seems that the green is not going away. There is always a way to get the most out of your pool season, without fear that green algae will be your guests at the next pool party.

If you are still having trouble getting rid of green algae, you can always contact us and he will guide you every step of the way.



How Long Does It Take A Green Pool To Clear Up After Shocking It?

It takes anywhere from a few hours to a few days for a green pool to clear up after shocking it. The length of time will depend on how bad the algae problem is.


Does Rain Cause Green Algae In The Pool?

Rain can cause algae blooms in pools for a number of reasons.

First, rain can wash debris and organic matter into your pool. This organic matter can then serve as food for algae. Additionally, rainwater itself is often loaded with nutrients that can encourage algae growth. Finally, rain can also lower the chlorine levels in your pool, making it easier for algae to take hold.

Be sure to properly maintain your pool’s chlorine levels. You may need to shock your pool more often during the rainy season. Additionally, be sure to remove any debris or organic matter that may have been washed into your pool after a storm. By taking these simple steps, you can help keep your pool clean and clear all summer long.


How To Remove Algae From Pool Walls?

Clean the algae off of your pool with a brush and then apply the appropriate algaecide to the surface. You must let the circulation be on for 24 hours before you vacuum or backwash.


How Dangerous Are Algae In A Green Pool?

Can you swim in the green pool infested with algae? The answer is that you can. But is it recommended? Well, not so much. Algae are accompanied by often harmful bacteria. It can cause problems with the skin, causing rashes.

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