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If you have a green pool, you probably won’t want to swim.  This article is here to help you to understand why your pool is green, as well as assist you with how to clean a green pool.

We’ll also show you how to balance your pool chemicals and use your pool’s circulation system so that you won’t have green pool water again.

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Image source: The Water Store

With regular pool maintenance you’ll begin to notice when your pool is turning green.  When you spend time doing daily maintenance you’ll notice any changes in your pool’s chemical balance and will be able to stop algae from growing instantly.  However, if you have been away and your pool has been left unattended, you may return home to a green swimming pool.

Follow this article to go from a green to a blue pool, restore water clarity and prevent future problems.

Why is has your pool turned green?

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You have green pool water because of a high level of algae in the water.  Algae forms due to a chlorine imbalance.  When you have enough free chlorine in your pool water, algae are unable to grow.

However, if your chlorine levels are low algae will begin to form, resulting in your pool turning green.  By restoring the balance of your swimming pool and shocking your pool, you will be able to get rid of the algae that have made your pool turn green.

How long does it take to treat your pool?

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If you have a green swimming pool you will want to treat it right away.  However, there is no way to turn green pool water clear again overnight.  It will take time and effort to turn your pool from green to clean.  The best route to take is prevention but many pool owners do end up with a green swimming pool at some time.

We will show you a proven method so that you can clear up a green pool in the quickest time possible.

The steps below will show you how to clean a green pool as best as you can within 24 hours.

24-hour steps to follow:

  • Catch any debris you can see in your green pool water. Use a pool net to do this.
  • Clean out your pool skimmers and put in clean nets or baskets.
  • Brush down the walls and floor of your pool to remove algae.
  • Clean your pump and filter.
  • Backwash your filter so that your pool can circulate water effectively.
  • Turn on your pool’s filter system.
  • Check your pH balance on your pool (which should be between 7.2 and 7.6). If your pH balance is out, your pool chemicals will not be able to work efficiently.  Make the adjustments if your pH level is out.
  • Add chlorine to your pool as a shock treatment. Follow the manufacturer’s instructions and ensure you have enough chlorine for the size of your pool.
  • Place flocculent in your pool’s skimmer basket. This will help you gather the debris remaining in your pool together and send it to the bottom of your pool.  Particles which don’t make it into the filter can be vacuumed up later.
  • Backwash your pool after 12 hours to get rid of any algae which may block your system.

After your pool circulation system has been running for 24 hours you should be rid of the algae or debris which has made your pool turn green.  If there is remaining algae at the bottom of the pool, now is the time to vacuum it up.

Steps for cleaning your pool

Test your swimming pool water

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When your pool is out of balance your chemicals will not be able to work properly.  Begin by testing your pool’s pH levels, alkalinity levels and chlorine levels.

If your chlorine levels are low (below 1 ppm) they will not be able to kill any algae in your pool.  Restore your chlorine levels by shocking your pool. This will help your chlorine levels return to normal.

Make sure your pool filters are working properly to remove all algae from the water and prevent it from growing.   When your chlorine and pH are balanced and your filters are working well, you won’t have the algae growth which leads to green pool water.

Even just a couple of days without regular maintenance can lead to algae growth and a green pool.

If your pool is turning green then there is little to no chlorine in your water.  If you are going to shock your pool, you will be adding a lot of chlorine.  Before you add chlorine, make sure your pH balance is approximately 7.2.

When your pH is out, chlorine will not work effectively.  If your pH levels are high, shocking your water with chlorine will turn your pool water milky.  Your pool will go cloudy once shocked because of the debris in the water.  However it will be very cloudy if your pH is out of balance.

You can use a high end pH testing kit to find out what your pH levels are when cleaning a green pool.  However, pH test strips will also do the job if necessary.  If your pH level is high, add a gallon of muriatic acid to your pool.  Optimal pH levels for swimming are between 7.2 and 7.6 but they can be a little lower for shocking.  Once you have shocked your pool and circulated your water for 4 hours, test your pool again.

Balance your pool’s chemistry

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Now that you have begun to clean your green cloudy pool it is time to test your pH balance again.  When killing algae a pH of approximately 7.8 is best.  A normal pH balance is between 7.2 and 7.8 but you would want it at the high end when killing algae.  Add chemicals to increase or decrease your pool’s pH balance depending on your results.

If you will be adding chemicals, turn on your pool’s filtration system so that the chemicals you add to the water will circulate.  If you need to increase your pool’s pH levels, add sodium carbonate to your water.  Do decrease your pH levels, add sodium bisulphate.

Use pH plus, pH minus and Alkalinity Plus to adjust the levels of your water.  You’ll need your pH and alkalinity levels to be correct before you can clear green pool water.

Check your pool filter

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Once you have got your chemical balance right, you will need to filter your pool.  You will want your pool’s filtration system to work well.  Check for debris or algae which may be blocking your system.  Make sure your filter is running smoothly before adding chemicals which will kill your algae.

If you leave your filter running for 24 hours you will have the best results while cleaning your pool.  You might have to backwash your filter two or three times to get rid of algae or debris which has clogged up the filter system.  When you are clearing algae from green pool water, backwashing your pool regularly is normal.

Remember that you cannot harm your pool by backwashing frequently.  Just remember to top up your water levels as backwashing removes water from your pool.

Running your filter consistently and backwashing regularly will help to clear up a green swimming pool.  Diatomaceous Earth filters will clear a pool more quickly than a sand filter will.  This is because the particles are finer and able to catch more debris.  You will need to add new diatomaceous earth to your skimmer after each backwash.

 Scrub the insides of your pool

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If you scrub the insides of your pool walls with a brush you will be able to move algae faster.  Scrubbing will break down the algae, which will allow the chemicals you place in the water to work faster.  Scrub your walls before you add any chemicals to your water.

If you see large areas of algae in your pool, focus on these areas most.  This will help you to break down the algae and send it to your filtration system.  You could catch large algae debris with a pool net.

If you have a vinyl pool, use a nylon scrubbing brush to prevent damage.

You may have to shock your pool more than once

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If your pool water is green due to large amounts of algae, you may have to give your pool a number of shock treatments rather than just one.  Start by adding 3 to 4 pounds of Granular Shock to your pool.  If you still have green pool water and see no improvement overnight, add the same amount the next day.

Keep adding the same amount until your pool goes from green to clean, turns milky or becomes a lighter shade of green.  Remember to keep running your filter and backwashing your pool while you work from green to blue pool water.

When you choose a pool shock, look for a product which has a high level of chlorine.  This will help you to kill algae and bacteria in your pool.  Follow the manufacturer’s instructions to ensure you get the best results.

Run your water through the filter until it turns from green to cloudy to blue.

Clean your filter regularly to prevent a build up of algae

As the algae in your pool dies, it will begin to lose its green colour.  It will also make its way into your pool’s filtration system, clogging up your filter.  Clean your filter regularly to get rid of algae debris.

Vacuum up the dead algae in your pool

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Brushing the side of your pool as well as shocking it with chemicals will result in a lot of dead algae.  These algae may float to the bottom of your pool.  You can vacuum up the old algae debris to remove it.  Adding flocculent to your pool will help the debris to come together, making it easier for you to vacuum up larger particles.

Run the filter to circulate your water

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Once you’ve shocked your pool and removed the debris you should no longer have green pool water.  Instead your water should be clear and blue.  Keep running your pool filter and monitor your chemical balance.  This will prevent your algae from coming back.  If you notice your algae returning shock your pool before your pool is green.  Shocking your pool again should keep algae away for good.

Maintaining your pool

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Once you’ve eliminated algae and your green pool water, there are some tips you can use to maintain your pool.  The most important tip is to keep your chlorine levels high enough to kill of any algae.  You can use a salt water chlorinator, a floatation system or an in-line chlorinator.  This will be more helpful than measuring out chlorine to throw into your water on a weekly basis.

Use the best filtration system you can afford

A diatomaceous earth pool filter is the very best for eliminating particles from your water.  It may be more costly at first but it will enable you to remove debris from your pool effectively.  This will save you time and money in the long run.

Maintain your pool filter

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A DE pool filter will need to be backwashed once a month.  Particles are fine and can accumulate debris.

A sand filter will need to be backwashed every two weeks.  Backwash your filter until the water runs clear.  You will usually need to backwash your filter for at least four minutes.  If you don’t give your pool filter enough time to clear itself properly, the dirty water will run back into your pool.

Cartridge filters have a fine membrane which can accumulate particles.  Unless you notice algae clogging up your cartridge filter, you can normally clean it once every three to four weeks.  You will also need to soak your cartridge filter in trisodium phosphate once every three months.

How to backwash a sand filter

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  • Switch off your pool pump.
  • Your sand filter has a dial which will determine the direction of the water flowing through your pool filtration system.
  • Move the dial to backwash. Press the handle fully down before turning the dial.
  • Close the valve that allows the water to return to the pool. Open the valve which allows the water to exit the system.
  • Make sure your waste hose is pointing in the direction you would like your waste water to go.
  • Turn the pool pump back on.
  • Run the pump for four minutes or until the water looks clear.
  • Once the water is clear switch off the pool pump.
  • Press the handle fully down and return the switch to normal operation mode.
  • Close the valve which allows the water to exit the system and open the valve which allows the water to return to the pool.
  • Turn the pump back on. Your pool’s backwash is complete.

If you have dirty green pool water is it better to empty out your pool and start again?

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If your pool is green and so opaque that you cannot see your hand when you dip it into the water, it may be better to start again.  The cost of replacing the water may be less than all the chemicals you need to create a healthy balance in your green pool water.  If your treatments fail and you have to replace your pool water anyway, this would create an additional cost.

If you are unsure whether or not to replace your green pool water, take a sample of the water from your pool to your local pool shop.  They will be able to test your pool water to find out the problem.  It may be that your pool has too much stabiliser.  Sometimes stabiliser is added to chlorine tablets to prevent them from being broken down by the sun’s rays.

If your pool has too much stabiliser it will prevent your chlorine from working efficiently.  This will lead to green pool water.  The only solution is to drain 80% of your swimming pool water and add fresh water.  Many swimming pools have to be emptied for this reason and in France; pools are emptied twice a year.  Once you replace your water you will be able to turn green pool water blue again.

Ending thoughts on how to clean a green pool

Green pool water happens to every pool owner at some time.  It may be frustrating to find your pool has turned green but you will be able to restore your pool to health again.  With the right chemical balance and an effective filtration system, you will have clear, sparkling blue water in no time.  Happy swimming season.

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