How to Clean a Green Pool the Easy Way

Nothing puts a dampener on your summer pool parties like slimy green buildup in your pool. While the green water is an eyesore, it is not that difficult to clean up if you put in some time and effort. This guide will teach you how to clean a green pool in a few easy steps.

Why Is Your Pool Green?

There is only one reason why your sparkling blue pool has turned an awful shade of green – an overgrowth of algae. A light shade of green means that the algae have just started to form. A deeper green means that you have a bigger algae problem on your hands.

clean a green pool

Reasons for Algae Formation

Improper pH Balance

The ideal pH level of your pool should be between 7.4 and 7.6. pH levels below 7.0 can make the water too acidic. Acidic pool water can cause swimmers irritation in the eyes and mucous membranes. It can also erode metal parts and the plastered finish of the pool.

pH levels higher than 7.6 can reduce the effectiveness of sanitizers causing algae formation, bacterial growth and skin irritations. So if your pool has turned green your pH levels are higher than they should be.

Low Pool Sanitizer Levels

Keeping your pool sanitized by adding chlorine, bromine or some other kind of pool sanitizer keeps your pool clean and germ-free.

If you haven’t been testing your pool water regularly you may have fallen behind on your sanitization schedule. Low levels of sanitizer in your pool water make it susceptible to algae formation.

Clogged Filters

Your filters need to be cleaned regularly if you want to keep your pool clean. If your filters have stopped working or if they are clogged with dirt and debris, the water in your pool will not be properly filtered. This makes it an ideal breeding ground for algae and all sorts of bacteria.

Changes in Weather

Algae multiply super quickly and thrive in hot and humid environments. A change in weather recently and a rise in humidity levels in your region could have triggered the algae growth in your pool.

Green algae will multiply quickly if they get some sunshine and warmth. So the slightly greenish hue you notice in your pool can quickly become a menace in hot weather.

Keeping the ideal pool temperature can help reduce the speed of reproduction of any algae or pool water bugs.

Methods to Clean Your Green Pool

Drain the Pool

Whether you need to drain your pool or not to clean up the algae depends on the severity of the algae growth.

If you can see about six to eight inches below the water despite the greenish hue, you can treat your pool chemically without draining it.

  • Vacuum up the algae from the pool.
  • Brush down the pool walls and floor with a heavy-duty algae brush.
  • Finish off with chemical treatments.

If the pool water is dark green or blackish in color, you have no option but to drain the pool completely and acid wash the pool’s surface to get all the algae out. It can be a good time to get rid of any calcium scale on the pool tiles – a good clean up!

If you think you don’t need to completely drain your pool to clean up your green water problems you can try these methods. They work when the problem isn’t too bad.

Lower Your Pool’s pH Level

The first thing you need to do before you begin sanitizing or chemically treating your pool water is to balance the pH levels. You can check the chemical composition of your pool water using test strips or liquid test kits.

High pH levels will reduce the effectiveness of the sanitizers. It is best to keep the pH below 7.2 before beginning the treatment to prevent the water from getting cloudy.

Add sodium bisulfate to reduce the pH level of the water. The amount of sodium bisulfate you need to add will vary depending on the acidity of your pool water.

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Shock Your Pool

Adding a super-concentrated chlorine solution to your pool will instantly kill bacteria and algae. You should make sure that your pool shock contains at least 70% available chlorine.

The number of times you need to shock your pool will also depend on the severity of the algae infestation. If you catch the algae in its initial stage, you only need to shock it once.

If the algae is a dark shade of green, it is recommended that you shock it three times to completely kill off the algae. If the water looks swampy and dark you might have to shock it at least four times. Learn how to shock your pool in this easy to follow guide.

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Clean Pump and Filter

Your filters will most probably be clogged by algae. You need to clean your filters properly before you start pumping water into your drained pool.

There are different kinds of pool filters available in the market. Check out which model you have in your pool and follow the product-specific directions to clean the filters.

After you have washed the filters, ensure that the water runs clean before moving on to the next step.

Floc Your Pool

Flocculants are additives that bind small particles together into larger clumps that are easier to clean.

Even after this intense cleaning session, minuscule particles of debris that are resistant to pool chemicals and small enough to pass through filters could end up clouding your pool.

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Adding a floc to the water will bind these particles together. You can just vacuum the clumps off the pool floor to clear your pool.

Kill the Algae

The chlorine shock will have taken care of almost all the algae in your pool. But as a precautionary step, you can use an algaecide to kill off any stray spores. Even small traces of algae can become a huge infestation if you don’t nip it in the bud.

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Tips for Preventing Green Pool Water

Check Filters and Pumps Regularly

If your filter is not working and the water in your pool remains stagnant for a long time your pool can become a haven for algae.

Ensure that your filters and pumping system are in working condition and regularly clean the filters to prevent algae growth.

Brush and Vacuum

Algae can creep up on you if you neglect the nooks and crannies of your pool. Make time every week to scrub down the walls and floor of your pool. Vacuum the pool to prevent any debris from building up.

Maintain a Healthy pH Level

The ideal pH level for your pool is between 7.2 and 7.4. Both the rise and fall of the pH levels beyond this range can have detrimental effects on your pool water.

High pH levels will result in algae formation. Low pH levels will cause eye and skin irritations as well as equipment corrosion.

Use a Pool Cover

Using a cover will prevent the wind from blowing in any debris and organisms into your pool.

Pool covers also minimize exposure to the sun. This will curb the rapid growth of green algae that might be lingering in some corners of the pool.

Maintain Proper Sanitizer Levels

Test your pool’s water once a week or every other day using test strips or a liquid test kit. This will help you keep track of the chemical composition of the water.

Top up your chlorine or bromine levels based on the readings to kill off bacterial growth and algae.

Sanitize your pool immediately if you notice a drop in the sanitizer levels as algae will thrive in an improperly sanitized pool.

Remember to check your pool stabilizer (cyanuric acid) levels. Pool stabilizer helps keep your chlorine working efficiently, protecting it from degrading from sunlight. See my guides covering cyanuric acid – and this one on how to reduce cyanuric acid levels in a pool. Lots of useful information!

Wrapping Up

Now you know how to clean a green pool I think you’ll understand that it can involve quite a bit of work, especially if you let things get bad. Prevention is much easier so save yourself some trouble!

Cleaning up pool algae can be quite a task, but preventing algae growth is super easy, especially if you regularly balance your pool water’s chemical composition.

Chemicals are your best friend when it comes to maintaining pool health. Keep those chemicals handy and you will have a sparkling blue pool all year round.

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years experience in pool care, plant care and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!