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Keep your pool water clean and clear with these expert tips
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Do you want to take a dip in your pool but the water looks green or cloudy? Algae in your pool is a common issue that makes the water dirty, but it’s so easy to get rid of the blooms and make your water crystal clear in just a few days. There are a few different ways to kill algae in your pool, and we’ll walk you through everything there is to know. Just keep reading to learn about the best pool algae cleaners and what you can do to prevent the algae from coming back.
Things You Should Know
- Scrub your pool walls with a pool brush to loosen algae stuck on the surface. Reduce your pool’s pH with sodium bisulfate until the levels are between 7.2–7.6.
- Apply 0.7 oz (20 g) of chlorine shock treatment for every 500 US gal (1,900 L) of water in your pool. Run your filter for 8 hours to circulate the treatment.
- Use a pool vacuum and clean out your filter to get rid of the dead algae leftover in your pool.
Steps
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Scrub the walls and floor of the swimming pool with a pool brush. Steel brushes work best on concrete pools while nylon brushes work better for vinyl pools. Brush vigorously to remove and loosen as much of the algae as possible. Pay special attention to the steps, behind ladders, and other nooks and crannies where algae tends to gather. [1] X Research source
- Brushing the algae off your pool surfaces helps the shock treatment work faster since the algae is floating in the water rather than stuck on the walls or floor.
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Reduce the pool pH to a level between 7.2–7.6. Fill a pool test kit with a sample of your pool water, and add about 5 drops of the pH indicator solution included in the kit. If the pH is above 7.6, which is common during an algae bloom, add a pH reducer such as sodium bisulfate to your pool according to label instructions. Wait at least 2–3 hours before testing the pool water again. [2] X Research source
- Stick with test kits that use tablets or droppers since they’re more accurate than paper test strips.
- Algae rarely grows in lower pH, but if your pool is below a pH of 7.2, add about 5 ounces (140 g) of soda ash for every 10,000 gallons (38,000 L) in your pool.
- If pH levels are back to normal but total alkalinity is above 120 parts per million (ppm), follow the instructions on the pH reducer label to bring the total alkalinity down between 80–120 ppm.
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Add chlorine shock treatment to your pool water. Use about 0.7 ounces (20 g) of shock treatment for every 500 gallons (1,900 L) of water in your pool. Wait until the evening after the sun sets to shock your pool so the UV rays don’t break down the chlorine. Dissolve the shock treatment in a bucket full of water, and pour it as close as possible to the algae on the sides and bottom of your pool. Keep your filter running for at least 8 hours after adding the shock treatment so it continues to cycle through the water. [3] X Research source
- Wear gloves, eye protection, and clothing that covers your skin whenever you handle chlorine products.
- If the algae has a mustard-yellow or dark black appearance instead of green, then add double or triple the shock treatment to your pool water to make it more effective.
- Avoid swimming in your pool for 2–3 days after applying a shock treatment since the high chlorine levels can irritate your skin and eyes.
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Test the pool’s chlorine and pH levels again the next day. Check on your pool the following morning to see if there’s dead algae, which will look brown or gray floating in the water or settled on the pool floor. Use another pool test kit to check the new chlorine and pH levels of the water, and make adjustments depending on your measurements. [4] X Research source
- If your chlorine levels are between 2–5 ppm but the algae is still there, then keep maintaining the same level for the next 2–3 days to kill off the rest of the algae.
- If chlorine levels have gone up slightly but are still below 2 ppm, add another dose of the shock treatment once it’s dark outside.
- If you don’t notice a change in the chlorine levels, your pool may have too much cyanuric acid. Continue adding shock treatment to your pool each day until you see an increase in chlorine. Alternatively, drain your pool partially to make the chlorine more concentrated.
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Brush and test your pool every day for the next 2–3 days. Use your pool brush to vigorously scrub the algae on the walls and floor that loosened up from the shock treatment. Over the next 2–3 days, the chlorine levels will continue to kill all the algae in your pool water, so test daily to maintain your swimming pool at the proper levels. Keep your pool at the following levels so the shock treatment continues to destroy the rest of the algae: [5] X Research source
- Free Chlorine: 2-4 ppm
- pH: 7.2 – 7.6
- Alkalinity: 80 – 120 ppm
- Calcium Hardness: 200 – 400 ppm
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Vacuum your pool to remove the dead algae. Once the green color disappears from your pool, hook up a pool vacuum to suck up all the dead algae. Run the vacuum across the bottom and along the walls of your pool in long sweeping strokes to suck up all the loose algae. [6] X Research source
- Move the vacuum slowly across your pool so it doesn’t kick debris back up into the water. If you move the vacuum too quickly, wait a minute or two for the algae to settle back on the bottom again.
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Clean dead algae out of your pool filter. Check your pool filter’s pressure gauge, and clean it if the levels are 10 PSI above the standard pressure (usually between 5–20 PSI). If you have a diatomaceous earth or sand filter, set the valve to backwash to flush out all the algae inside. If you have a cartridge filter, remove it and clean the cartridge with a jet attachment on your hose. [7] X Research source
- If you do not clean the filter thoroughly, then the dead algae may block the filter and prevent your pool water from circulating.
- Monitor your pool filter system closely during the entire shock treatment since the dead algae may quickly build up inside the filter and need to be cleaned out more frequently. [8] X Research source
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Improve your pool’s circulation to handle small spots of algae. If small clumps of algae form but don’t spread to the rest of the pool, there may be areas of stagnant water. Check that the water jets inside your pool are active and circulating water through your pool. Point the jets downward so the water at the bottom of your pool moves through the filter system to kill any algae growing there. [9] X Research source
- Check the skimmer basket on your pool’s filter as well since clogs could prevent water from moving through your system.
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Use pool flocculant to collect loose algae before vacuuming. A flocculant or “floc” clumps the algae together so it’s easier to suck up and remove from your pool. [10] X Research source Shake the bottle of flocculent and follow the manufacturer’s mixing instructions to add the required amount for the size of your pool, usually around 16 fluid ounces (470 ml) for every 20,000 gallons (76,000 L) of pool water. Pour the flocculent directly into your pool’s skimmer and run your filter for 4 hours. Then, let the water sit for 12–14 hours before vacuuming the bottom of your pool. [11] X Research source
- Avoid using pool floc if you have a cartridge filter since it could cause a severe clog.
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Treat the pool with algaecide if it has cloudy water. Algaecide contains chemicals that kill and destroy algae blooms in your pool. Follow the instructions on the algaecide package to find out how much to add to your pool, which is usually around 1 gallon (3.8 L) for every 50,000 gallons (190,000 L) of pool water. Add the algaecide to your pool, and let it circulate for 24 hours. After that, simply vacuum up all the dead algae on the bottom of your pool. [12] X Research source
- If there’s still algae growing in your pool water, then repeat the treatment the next day.
- After adding algaecide, wait at least 24 hours before adding other chemicals or treatments to your pool.
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Shock your pool once a week. Find an evening each week to apply 1 pound (450 g) of shock treatment for every 12,000 gallons (45,000 L) of pool water. Spread the shock treatment in the deepest section of your pool and run the filter for 4–8 hours so the treatment circulates through your entire pool and kills any algae before it has the chance to bloom. [13] X Research source
- If you notice any shock treatment granules at the bottom of your pool after 15 minutes, use a pool brush to spread them around and help them dissolve.
- After a weekly shock treatment, wait at least 15 minutes before going back in your pool when the chlorine levels are between 1–4 ppm.
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Clean your pool weekly. Make time to check and empty the skimmer basket on your filter so it doesn’t get clogged and prevent water from circulating in your pool. Use your pool brush to scrub the walls and floor of your pool as well to ensure that no algae sticks to the surfaces. [14] X Research source Then, make sure you vacuum your pool floor weekly to keep your pool water clean and clear.
- If you have a pool party or if there’s a heavy storm, then clean your pool right away before algae has a chance to form.
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Circulate your pool water for at least 8 hours a day. Since algae easily grows in stagnant water, turn your filter and pump on so it’s running throughout the day. Make sure the jets point down toward the floor so the water at the bottom of your pool moves through the filter as well. [15] X Research source
- If you have a larger pool, like one that’s Olympic-sized, then run your filter for a few hours longer to fully circulate the water.
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Test and maintain your pool water chemistry every week. Algae will not grow in your pool as long as you keep on top of your pool chemistry. Test your pool each week for free chlorine levels, pH, alkalines, and cyanuric acid to make sure they’re all at a reasonable level. The faster you catch a problem with your pool’s chemistry, the easier it will be to correct it before algae starts growing. [16] X Research source
- If you just got rid of an algae bloom, then test your pool water every day for the next 1–2 weeks.
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Add an algaecide as a preventative every 3–5 days. Use a maintenance dose of algaecide, which is usually about 1 US quart (0.95 L) for every 50,000 gallons (190,000 L) of pool water. Pour the algaecide into your pool skimmer and let it sit for about 24 hours. After that, vacuum your pool to get rid of any dead algae gathered at the the bottom of your pool. [17] X Research source
- Some algaecides may have different concentrations and usage instructions, so always follow the directions on the package.
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Apply a phosphate remover to your pool water. Use a phosphate test kit to check if there are any present in your pool. If the test comes back over 300 ppm, follow the mixing directions of a commercial-strength phosphate remover and pour it into your pool. Run your filter to circulate and get rid of the phosphate remover over the next day or two so the levels go down. After that, shock the pool to restore the chemical balance of your pool. [18] X Research source
- Algae feed off phosphates that get in your pool water from leaves, twigs, or run-off from landscaping, so it’s important to get rid of them. [19] X Research source
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Community Q&A
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QuestionHow do I prevent DE powder from entering the pool?Community AnswerIf DE powder is entering the pool, one or more of your septum elements is torn or not properly connected to the header.
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QuestionCan I empty an above ground pool without it caving in?Community AnswerYes, it will not cave in if the top bars are all in place. But do what you have to do and refill as quickly as possible. Letting the vinyl liner dry out in the sun can allow it to shrink. Fill the pool on an 80 degree, sunny day ONLY. Don't fill at night.
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QuestionHow do I get algae out of my pool without vacuuming?Community AnswerYou can brush it, causing it to stir up into water, and then let the filter grab it. However, if you do that, you're going to have to backwash it a few times throughout the process.
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Tips
- Heat and sunlight break down chlorine and encourage faster algae growth. Keep a closer watch on chlorine levels during hot, sunny weather. [20] X Research sourceThanks
- In the winter, invest in a mesh pool cover that will prevent debris from entering your pool, yet allow water to pass through. [21] X Research sourceThanks
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Warnings
- Avoid swimming in your pool if there’s an algae bloom since it could contain bacteria or toxins. [22] X Research sourceThanks
- Stay out of your pool until the chlorine level in the water has returned to a safe level of 3 ppm or less. Otherwise, it may irritate or burn your skin. [23] X Research sourceThanks
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Expert Interview
Thanks for reading our article! If you’d like to learn more about swimming pools, check out our in-depth interview with Rob Litman .
References
- ↑ https://mag.pioneerfamilypools.ca/media/mageworx/downloads/attachment/file/h/0/Algae-Treatment-Sheet-1-1.pdf
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
- ↑ https://www3.epa.gov/pesticides/chem_search/ppls/001258-01237-20151005.pdf
- ↑ https://poolsandcues.com/wp-content/uploads/2023/08/Clearing-Up-a-Pool-with-DE-Filter.pdf
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
- ↑ https://youtu.be/rQNRW_Ka8zo?t=220
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
- ↑ https://www.pentair.com/content/dam/extranet/nam/pentair-pool/residential/filters/clean-and-clear-family/clean-and-clear-plus/clean-and-clear-plus-guides-manuals/clean-and-clear-plus-install-guide-english.pdf
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
- ↑ https://youtu.be/mxvkjou2aN8?t=89
- ↑ https://youtu.be/lGBCIKPB5Rg?t=106
- ↑ https://www3.epa.gov/pesticides/chem_search/ppls/001839-00087-20020826.pdf
- ↑ https://www3.epa.gov/pesticides/chem_search/ppls/067262-00046-20220907.pdf
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
- ↑ https://www.bobvila.com/articles/cloudy-pool-water/
- ↑ https://youtu.be/eW9gpfVtDhs?t=351
- ↑ https://www3.epa.gov/pesticides/chem_search/ppls/001839-00087-20020826.pdf
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
- ↑ https://mag.pioneerfamilypools.ca/media/mageworx/downloads/attachment/file/h/0/PFP-Phosphate-Guide.pdf
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
- ↑ https://gohlkepools.com/documents/BrochuresPDF/CoveringWithMeshCover2-17.pdf
- ↑ https://www.waterboards.ca.gov/water_issues/programs/bluegreen_algae/docs/workgroup110805/bgadetailedfactsheet.pdf
- ↑ https://www.nitt.edu/home/students/facilitiesnservices/sportscenter/swimmingpool/SwimmingPoolMaintenance.pdf
About This Article
Article Summary
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To eliminate and prevent green algae in a swimming pool, start by adding an extra dose of chlorine to your pool to shock the algae and stop the bloom. Let the chlorine work overnight, then test the pH levels of the pool in the morning to see if the pH is back to normal. Next, use a pool brush to scrub algae off the walls of the pool, then vacuum up any dead algae. To prevent it from blooming again, test your pool’s chemical levels daily and make adjustments as needed. For more ways to prevent algae in your swimming pool, read on!
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Reader Success Stories
- "Educational article! I know having algae in the pool is not hygienic, but didn't know all the consequences of poor treatment and details of follow-up. Being in the management committee of the condo community, this will help me manage the pool conditions." ..." more
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"Educational article! I know having algae in the pool is not hygienic, but didn't know all the consequences of poor treatment and details of follow-up. Being in the management committee of the condo community, this will help me manage the pool conditions."
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"Our pool is above ground. Never have we had algae like this, and treat it daily. Now we are pumping it down to empty and will clean all over. The walls that we now can see are covered with green slime in certain spots."
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"Last year, we had pool maintenance. This summer, I was determined to learn and do it myself. This article answered many questions. The Community Q&A answered the rest. What a lifesaver!"
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"We have just understood that in this very hot weather we probably need to cover the pool when it is not in use, to prevent the algae regrowing as fast as we clear it."
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"This is a one-stop article, the numbers and test methods are accurate. Liquid chlorine is my #1 additive. I test once or twice a week, and always after it rains."
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