How to Clean a Green Pool

Sometimes life gets away from you and your regular chores slide a bit. Or the weather hasn’t been conducive to outdoor swimming, and you’ve slacked off on your maintenance. But now the sun is out and it’s time for swimming! You’ve opened your pool, and it’s green. The longer pool maintenance has been ignored, the more likely your pool is to be green. Let’s look at why this happens and how to clean a green pool fast!

How to Clean a Green Pool

Why Your Pool is Green

In most cases, the culprit is algae overgrowth. Algae doesn’t take long to start blooming in pool water. Temperature, contaminant levels, sunlight exposure, and circulation all play a role in how fast you develop algal blooms. It can develop in a matter of hours or take weeks.

For algae to thrive, it only needs sun and food. Pools are ripe with food, especially if it hasn’t been cleaned. Algae can even feed on chlorine particles. he hotter the temperature, the faster algae reproduce, and before you know it, you have an infestation.

The green color that you see comes from chlorophyll inside the plant, which it uses for photosynthesis.

The primary causes of algae overgrowth in swimming pools are:

  • Improperly balanced pH. A pH level that is too low will erode the materials inside your pool and cause skin and eye irritation. If it’s too high, bacteria aren’t get killed, and neither is algae. Out of balance pH levels lead to water discoloration, no matter which direction on the pH scale your water is leaning.
  • Clogged filters. Filters that don’t work don’t keep pool water clean. Pools with dysfunctional filters breed bacteria and algae.
  • Weather changes. Drastic weather changes are the hardest factor to deal with because you can’t control them. You can clean your pool, maintain pH, and keep your filter in good working condition, but you can’t control hot, humid weather. If you’ve recently experienced a weather change, this could be the cause of your algae.

What is so Bad about Algae?

In and of itself, algae isn’t toxic to swimmers. The problem is that it hosts bacteria, such as E. coli, that is harmful.

In addition, algal blooms reduce visibility in your pool which can be a safety hazard and clog up pool filters to render them useless in filtering your water. Long-term algae growth also has the potential to eat away and stain your pool walls.

Because bacteria are microscopic, they can hide out in small cracks and crevices, on ladders, inside liners, and a million other tiny spots you can’t see. Once it’s there, it’s hard to get rid of, so it’s best to prevent it from ever getting there in the first place.

6 Steps to Getting Your Pool Algae Free

Once you’ve determined the reason for your slimy, green pool, it’s time to clean it up. If there’s a mechanical failure in your pool filtration, fix that first. If it’s just that you’ve been neglecting maintenance, it’s time to get back on track. Either way, here are the steps you can take to clean up your green pool.

1. To drain or not to drain

If the color of your pool water is very dark green, bordering on black, it’s properly more effective to drain all the water and start over. You’ll need to acid wash your pool walls before refilling to avoid regrowth. You may or may not need a professional to help you with this.

If you can see about 6 inches below your water’s surface, you can probably clean up your water with chemicals. So, roll up your sleeves; it’s time to get to work!

2. Remove excess debris from the water surface

Scoop as much of the algae out of your pool as you can. You will need a telescopic pole with a skimmer net to do this. Start at the surface and work your way down. The more algae you can physically remove from your pool, the better. Keep scooping until you’re no longer picking up substantial amounts of debris in your net.

3. Decrease the pH level of the water along with your chlorine levels

Test your water to find out the pH first. Chances are you have alkaline water or a high pH. Since your water is green, it’s safe to assume that your chlorine levels are way too low. If your pH is way too high (which it probably is), you can use a pre-mixed pH reducer or muriatic acid to bring it down.

Normally, you want your pool’s pH level to sit about 7.5. In this case, we want it a bit lower, around 7.2, for optimum cleaning.

4. Shock and shock again

It’s important to shock your pool with granular chlorine to clean up organic contaminants. You can use liquid chlorine to shock your pool as well.

Distribute it evenly around your pool and let your filter pump run to distribute it. You will want to keep your pump running from this point on to ensure your chemicals are thoroughly distributed. Leave your pool water circulating for at least an hour before re-testing the chlorine levels.

Most pool shocking products provide instructions for use on a regular basis. From a scientific perspective to de-structure the DNA of algae, you will need to bring the chlorine levels of your water to 30 ppm.

Add shock and test. Repeat the process until your water has the right level of chlorination. You might have to do this several times. The severity of your algae growth will determine how long this process takes.

5. Pump and filter

Once you’ve balanced the pH and reached a 30-ppm level of chlorine, you need to pump and filter your pool water to regain balance. The type of filter you have will determine the method you use to do this.

If your pool is equipped with a DE or sand filter, you need to backwash your filter before doing anything else. The basic steps to backwash your filter are:

  • Shut off your pump, attach a backwash hose, and check for closed valves in your wastewater line.
  • Slide your push-pull valve or turn on the multiport valve handle.
  • Turn on your pool pump. There should be water flowing out the backwash pipe or hose.
  • Backwash until your water runs clear. It usually takes about 2-3 minutes.
  • Shut your pump off, turn the valve back to the filter, and turn the filter back on.
  • Notice the lower pressure on your filter tank and the increased flow rate.

6. Floc your pool

Once you have pumped, filtered, or backwashed your pool, your water is probably still cloudy from residue. There are some microscopic particles that are resistant to pool chemicals, and they are the cause of this cloudiness.

Flocculent helps you clump the debris together. Sometimes marketed as “clear-it” or “clarifier,” flocculent will clump all the leftover debris particles together so you can vacuum them off the pool bottom.

7. Re-test chlorine levels

Once you have completed the first six steps of this process and are noticing clear pool water, let your pool sit overnight. Then re-test your chlorine levels. If you are losing free chlorine, there is still algae spores present in your pool. This leads us to the last step of removing all the leftovers you can’t see.

8. Kill off the algae

Your water should be crystal clear by now, and performing another step probably seems unnecessary. However, this extra step might just prevent you from having to repeat this entire algae-removal process next week.

Algae grow quickly and only need a few spores to start the takeover of your swimming pool. Anything you leave behind and don’t kill will spread fast. Use an algaecide to kill off any remaining spores and continue treatment to prevent regrowth.

Continued Pool Maintenance

Maintaining your pool regularly will help you prevent algae and debris from getting out of control. They are some simple steps you can take to keep your pool water clean and clear:

  • Check your pumps and filters frequently. Stagnant water is a happy home for algae to grow, so make sure that your filter and pump system are working properly and circulating your water.
  • Brush and vacuum debris on a weekly basis. This will prevent any bacteria or dead algae from regrowing.
  • Maintain normal pH levels in your water. Your pool’s pH level should be checked at least 2-3 times per week, along with testing your chlorine levels. It is recommended to maintain your pH levels between 7.4 and 7.6.This should prevent algae spores from having the opportunity to bloom.
  • Make use of a pool cover. A pool cover is the best way to prevent dirt and debris from landing in your pool. It will also keep out UV rays that can supercharge algae growth rates.


Preventing algae growth is easier than clearing it up. Try to make the time each week to provide some TLC to your swimming pool as this will prevent you from having to clean up a yucky, green mess.

But if the worst has happened and your pool is green, we hope the tips provided in this article help you to get it cleaned up so you can get back to enjoying your backyard swimming pool!

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