Filthy backyard swimming pool and patio

How to Effectively Clean a Green Pool

Is your pool looking a little green? Pools are generally chlorinated or contain salt water for a reason. Uncontrolled, unsanitized fresh water is the ideal environment for bacteria, and the algae on which they feed, to thrive. Algal blooms may result in murky, green waters that are hardly the ideal environment for taking a dip.

Besides looking uninviting, when left untreated for too long, algae issues can adversely affect the construction of your pool. Unsightly stains on your fiberglass, tiles, or pool liner may result, as well as untreated water posing a risk to swimmers. If algae and bacteria go unchecked, those who risk a dip may catch an eye or ear infection or a skin rash.

Whether you’ve spotted a few green patches, or your pool is looking more like a pond than a place to relax with family and friends, we’ve got you. Follow these tips on how to clean up a green pool quickly and effectively.

In This Article

What Is Pool Algae and How Does It Form in Pools?

Green pool algae are a live organism called a single-celled chlorophyte. These plant-like organisms are microscopic, only becoming visible to the human eye when millions are present in a formation. As the name implies, chlorophytes make their own food via photosynthesis, just like land-based plants. The chlorophyll is what gives algae its unique green hue.

Algae forms in places with just the right conditions, particularly wherever there is adequate moisture and sunlight. However, algae have adapted to survive in many places, including on land, symbiotically with fungi, and in saline water. Additionally, algae can come in other shades, such as black and yellows — and even be bioluminescent.

Another fun fact is that algae aren’t all bad. It’s often used to treat still and wastewater, aerating it and improving clarity. The main reason algae spores in a pool are dangerous is because they’re the perfect food (and attractor) for harmful bacteria.

How to Clean a Green Swimming Pool

If your pool is already green, preventative measures will no longer be effective. You need to get your pool clean again before you can swim and get back to your regular pool maintenance routine. Here’s how to clean green chlorine, saltwater, or mineral pools effectively.

How to Clean a Green Chlorine Pool

Chlorine pools are some of the most common types of swimming pools located in homes and at public facilities. Follow these easy steps to clean your green chlorine swimming pool.

1. Clear Out Pool Debris

Fall leaves and debris floating on the surface of outdoor swimming pool

Leaves and other large debris need to be removed prior to treating a green pool. Depending on how bad the pool debris’ is, use a leaf net or other suitable pool cleaning equipment to get it out. However, do so while creating as little movement as possible to avoid disturbing and mixing the sediment with the water.

2. Brush Your Pool Walls of Algae

pool brush next to a dirty swimming pool

After any larger debris is out, it’s time to scrub any algae growing on the pool floor or wall off. You can use a pool brush tool, preferably with a pole, to ensure you don’t touch the water. The aim of brushing algae off is to suspend it in the water. So the shock treatment and chlorine can do their job killing it off, and it is easier to filter out.

3. Adjust Your Pool pH Balance & Alkalinity Levels

Check the pH of a private swimming pool

Before treating your pool, you also need to make sure its pH balance and alkalinity levels are just right. Doing so will ensure the chlorine and chemical treatment can work as effectively as possible. Test and treat the water accordingly before you go on to the next green pool cleaning steps. You should always test and maintain pool pH and alkaline levels to prevent algae.

4. Shock-Treat Your Green Pool

Tester with tablet and powder of chlorine

A green pool needs a lot more than a regular dose of chlorine or pool chemicals to get it back in tip-top shape. Shocking the pool with up to five times as much chlorine as usual usually does the trick:

  • Choose the right shock treatment; liquid or powdered.
  • If powdered, make sure to mix the treatment thoroughly with water until all granules are dissolved before adding it. Otherwise, the granules may drop to and damage the bottom of your pool.
  • If a liquid treatment, simply pour it into the pool (or follow the directions on the pack if to the contrary). Just make sure to spread the treatment around, not in one place, to ensure even distribution throughout.
  • Keep doing shock treatments for a few days until the pool water color changes from green to clear.
  • Do note that, ideally, you should do shock treatments after the sun goes down to get the best results. If done during the day, the sunlight and warmth can affect the chemical balance and results.
  • You should also avoid swimming in or dipping your limbs into a pool that is being shock-treated. Doing so could result in chemical burns, respiratory issues, and eye and skin irritation. It is only safe to do so when your chlorine tester level reads 3-5 ppm or less.

5. Clean Your Pool Filtration System

While you’re busy shocking your pool, don’t forget about your pool filtration system. Treat it at the same time that you’re shock-treating to ensure even cleaning. Ideally, add liquid chlorine to it and let that filter back out into the pool water.

6. Filter & Backwash Your Pool

Pool-cleaning professionals will typically filter out the green water and finer sediment when cleaning a green pool. Be sure to run your pool filter between shock treatments, as well. Do so for at least 8 hours, and even 24/7, until your pool is clear. Backwashing the filter is also necessary to clear out algae in it that may contaminate pool water later.

7. Add an Algaecide

Once your pool is treated, do top it up with an algaecide. This treatment will kill off invisible algae spores that may cause a recurrent algal bloom soon after. You can also add regular algaecide treatments to your pool-care routine if you haven’t done so so far.

How to Clean a Green Salt Water Pool

As saltwater pools are also technically chlorinated, you can follow the above steps to clean yours when green. Saltwater pool systems turn saline water into hypochlorous acid (HClO) and sodium hypochlorite (NaClO). Or what we know as chlorine. So, you can treat them with shock solutions. Ideally, pick treatments that are safe for saltwater pools, such as calcium hypochlorite shock.

How to Clean a Green Mineral Pool

Green mineral pool water is more difficult to clean and shock, especially using chlorine-based shock treatments. You can follow all the above steps to clean a mineral pool, except shocking and treating with chlorine. Chlorine levels may get too high, damaging the mineral cartridge, system, and balance. Shocking the system with non-chlorine treatments is the safest option.

However, finding the right mix of chemicals while also adequately killing off bacteria and algae spores can be challenging. Instead, some pool professionals suggest removing the mineral system cartridge and shocking the pool water with chlorine chemicals. Then, reinstalling the cartridge later when chlorine levels have dropped to safe levels.

How Can I Prevent Algae From Forming in My Pool?

Fresh water is generally safe to swim in but, if contained, should be treated regularly. As still water doesn’t aerate or get replenished frequently like streams or rivers, contaminants and bacteria can easily build up in it. Ideally, pool water should be kept clean, alkaline, and pH-balanced to reduce the chance of algae forming. The preventative treatment best suited to your pool will depend on your particular setup.

How to Prevent Algae Forming in Chlorinated Pools

Chlorinated pools rely on both chemicals and the right pH and alkalinity balance to stay sanitized. Regularly treating your pool with just the right amount of chlorine is necessary. However, when the pH and alkaline balance of a chlorine pool is off, this will affect the efficacy of the chlorine added. A pH balance of 7.4 to 7.6 and alkalinity of 100 and 150 ppm is ideal.

How to Prevent Algae Forming in Salt Water Pools

Saltwater pools also deter bacteria and algae formation but do so through chlorine produced by a saltwater generator. The best way to ensure saltwater pools don’t develop bacteria and algae is to maintain adequate saline levels. Filtering your saltwater pool regularly also helps clear out as many stray algae spores as possible.

How to Prevent Algae Forming in Mineral Pools

Mineral swimming pool water is similar to the water of saltwater pools. However, instead of salt, the active ingredients in these pools are commonly minerals such as magnesium chloride, sodium chloride, and potassium chloride. Equally, the most efficient way to keep green algae at bay in mineral pools is to keep mineral levels balanced. Additionally, make sure that you filter the pool regularly.

Other Effective Ways to Minimize Algae Formation in Swimming Pools

  • Algae spores typically get introduced to pool water by items carrying these organisms. Avoid using old, algae-stained pool toys, cleaning equipment, or swimwear in swimming pools. Also, try to sanitize and clean any tools, toys, or swimsuits with bleach or detergent to kill spores between uses.
  • Rainwater can both carry algae spores and imbalance swimming pool water when too much gets in yours. As such, it’s necessary to treat your pool after a storm and clean algae-attracting debris from it. If you recently filled up your pool with fresh water, treatment will be necessary, as well to restore the chemical balance.
  • Sunlight and warmer water temperatures offer sustenance and the ideal habitat for algae to thrive. Keep an eye out for and quickly deal with algae formations during warmer, hotter months to avoid their spread.
  • Algae often grow on the walls and floors of swimming pools. Regularly brushing your pool with a stiff-bristle pool brush will loosen these formations, deterring their growth. Vacuuming, filtering, and backwashing your filter regularly can also help reduce algae spore numbers.


A green pool may spell a short break from enjoying some fun in the sun. However, with a little elbow grease and the right tools, you can have those crystal-clear waters back in no time. Just remember to stay safe, test, maintain, and call in the professionals if you feel you’re in over your head.

Caitlin Greyling

Caitlin Greyling is a professional writer and editor with a fine art, design, and photography background — focusing on sustainability, climate change, equality, travel, tech, culture, and societal issues. She’s currently studying journalism with the NCTJ and has written for The Daily Mail, Durability Matters, CNN, PictureCorrect, Pilot Plans, and more.

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