Rob is a pool-service industry professional with over 20 years of experience.
Help! The Pool Is Green!
Treating a pool that has turned green? This article will take you step-by-step through how to get that nasty pool in shape. I will also cover some basic chemistry and filtering tips to prevent this from happening again.
What Makes the Pool Green?
Algae makes your pool green, and a chemical imbalance lets the algae grow. If there is enough free chlorine in the pool, algae will have a hard time forming. If for some reason the chlorine can’t build up to a high enough level, algae will grow. That's why you shock your pool with chlorine as part of the six-step process below. If the green comes back, you can adjust the levels of other chemicals besides chlorine, as there is more to pool water chemistry than chlorine alone.
Six Steps to Cleaning a Green Pool
- Determine whether your water chemistry can be fixed, or if it's too far gone.
- Test the water to determine the pH balance.
- Shock the pool.
- Pump and filter the pool to regain balance.
- Brush and filter the pool again.
- Maintain balanced chemistry.
Each of these steps is described in detail below. All information is based on an in-ground home pool of average size, from 12 to 15 thousand gallons.
Step 1: How Green IS Your Pool?
If it's too green, these six steps won’t be enough; you may need to have the pool drained and acid-washed, instead of shocked. I have seen many pools that were not just green, but black. In severe cases like this, it is more cost-effective and less time-consuming to simply drain the pool and have it acid-washed, even though it costs money to refill the pool.
This is my general rule for determining whether the pool can be treated chemically or needs to be drained: if you can see at least six to eight inches below the surface of the water, most likely the pool can be treated chemically. An example is in the photo below; you can see the top of the first stair down into the pool.
Once we establish that the pool doesn't need to be drained and can be treated chemically, we can go from there.
Step 2: Testing the Water
If the pool is green, there’s obviously little or no chlorine in the pool, so if you are going to shock it you will be adding a lot, so testing for chlorine is not very important. But you should test for pH, because if the pH is very high, the shock will turn the pool cloudy. A shocked pool will be cloudy anyway until all the dead algae and other solids are filtered out, but high pH will cause a VERY cloudy pool.
To find out the pH, I prefer to use a high-end test kit, but the cheap test strips will at least give you an idea if your pH is high or low. You want it to be low: 7.2 or lower.
If the pH is high, add one gallon of muriatic acid, which should be enough. Don't worry that you may have added a little too much, because the pool can be a little acid (low pH) for swimming purposes but still at a good pH for shocking. Test the pH again after shocking and four hours of circulation.
Step 3: Shocking the Pool
Once your pH is 7.2 or below, you are going to shock the pool with granular chlorine (calcium hypochlorite). I suggest purchasing a 25-pound container of granular chlorine, rather than the individual one-pound bags they sell at pool stores or large chain stores. You'll save a great deal of money, and you will need chlorine in the future for small doses from time to time. Use five pounds of granular shock, or 10 gallons (four 2.5-gallon jugs) of liquid chlorine. With the filter pump on, broadcast the chlorine evenly over the water, covering the entire pool surface, until all five pounds of shock, or all ten gallons of liquid chlorine, have been used. Be sure to use a good algaecide as well, which you can add after a few hours of circulation. You can also add a floccing agent at this point to cause the dead algae particles to clump together.
I wrote a follow-up article about shocking the pool that answers some of these questions in more detail:
- How much shock should I use?
- How long should I run the pump after shocking?
Read More From Dengarden
Step 4: Pumping and Filtering
What type of filter do you have? Follow these steps for your type of filter.
- Diatomaceous Earth (DE) Filter: Before doing anything else, backwash the DE filter. Add fresh DE powder. Then shock the pool as explained above, and run the pump for 24 hours. Make sure the pool drain is not obstructed by leaves or other material while this pumping is going on. If the pool is so green you can't see the drain, just run a brush over the approximate location of the main drain at the deep end of the pool.
- Sand Filter: Same as for a DE filter, except the backwash time should be a minimum of five minutes.
- Cartridge Filter: Make sure it's in good condition and rinsed thoroughly. See note in Step 4 below about cartridges.
Step 5: Brushing and Filtration
After 24 hours of chemicals and circulation, you will see an amazing transformation. Your pool should not be green anymore. But it will still be cloudy, and it will need a lot of brushing and filtration for the next few days. There will probably still be a few stubborn isolated green areas that need some brushing.
It will take a while for the cloudiness to go away.
- For a sand filter, it will take a week or more.
- Cartridge filters will need to be cleaned more often than other filters during this process: twice a day for at least two days, or until the pool is clear.
- If you have a DE filter, and the cloudiness does not clear up, your filter may be clogged and need repair or maintenance.
Step 6: Maintaining Your Pool in Balance
Tips for maintaining your pool:
- Make sure you have a reliable chlorinating system, whether it is an in-line, floater, or salt system. Chlorine needs to be in the pool always. Throwing a jug of liquid in it once a week isn't a good way of maintaining the pool. A simple tablet chlorine floater is very effective.
- Use a water clarification solution.
- Clean your filter. DE filters are by far the best filter to have. Although a bit more costly to purchase at first, they will save you both time and lots of money in the long run.
How often to clean your filter:
- DE filters: Backwash once a month.
- Sand filters: Backwash once every two weeks. Be sure to backwash your sand filter for a minimum of four minutes; otherwise, you will see filthy water shooting back into the pool.
- Cartridge filters: Clean it every three to four weeks, unless you see algae in the pool, in which case you should clean more often. Here's more about how to clean a cartridge filter. Soak in trisodium phosphate every three months.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
Question: I shocked the pool, and then waited over 12 hours to go in and vacuum. At this point, the water was a blue cloudy. Towards the end of vacuuming, the pool is now green. I backwashed the filter, and let the pump run for over 12 hours. This morning I went out, it's still green, but clear enough to see to the bottom of the pool. I can see what I believe is algae on the pool floor. But I know if I go in to vacuum, it will be green again. What do I use, what do I do for this?
Answer: So what is happening is that when you vacuum, much of the "green" is shooting back into the pool. You mentioned backwashing, so you either have a sand filter or a de filter. If a sand filter, this makes sense. In either case, the pool needs to be vacuumed to waste so that EVERYTHING is being vacuumed to waste and not returning to the pool. Some systems just have a valve to open to drain the pool, but depending on the plumbing, sometimes when this is open, some flow can continue through the filter and out the pool returns (even though some of it is going to waste). If you can't vacuum all to waste, keep the filter clean (daily) and the pump running for as long as it takes to filter out. But it sounds like you need a floccing agent and a way to be able to vacuum to waste. Check this article on using a flocculant:
Question: My pool was so clean all the time, but I changed to another company, and my pool is too green. The company says that somebody used sun creams inside the pool, but they haven't fixed the problem yet. What can I do?
Answer: Suntan oil, lotion, sunscreen, etc., clog the filter. Cartridge filters absorb this the most. Sand filters are not highly affected by this. DE filters will absorb all of the oils, but will just need to be backwashed more frequently. What can you do? Keep the filter clean. Make sure there is plenty of flow. As long as the chemicals are balanced, then make sure the pump and filter are flowing at full capacity. Sunscreen type of products will cause build-up on the filter reducing the flow. Clean or backwash your filter. If it's a cartridge filter, the cartridge may need to be replaced
Question: Why did my pool turn green after I missed a day or two of treatment?
Answer: Try checking these things: The filter. Make sure it's clean, and there is plenty of flow. Chemistry: Have the water tested for phosphates and treat as needed. Check the stabilizer and make sure it's under 50. If the chemistry is balanced, I suspect a bad filter and lack of flow.
Question: The pool store measured my copper level at .3; they said this is what is making my pool green. My pH was high, and the chlorine was low. I poured a bottle of Metalfree in but after 24 hours, there was still no change. Do you have any suggestions?
Answer: I would question the integrity of the pool store you visited since copper will not turn a pool green. It sounds as though you were the victim of an "upsell". Although it is good to keep your pool free from metals, this is not why the pool is green. Low chlorine and high pH makes more sense. To balance the chemistry (pH, chlorine, and alkalinity), I recommend the pool also be tested for phosphates. Make sure the pool filter is clean and working properly with good flow. (Does the cartridge filter element need replacing? Is the sand filter working properly? Is the DE filter holding the DE powder?) If you have an in-ground pool with a concrete type surface with a serious copper problem, then blue or teal color stains will be visible. A vinyl liner will make it difficult to detect any "metal" type effects.
Question: Can water temperature be too high to get accurate chemical readings from a pool?
Answer: No. Even in a spa that usually runs 100-104 degrees Fahrenheit, an accurate chemical reading will be available. Warm water will not create any false readings regarding chemistry provided the test kit being used is not out of date. DPD test kits (kits that use liquid "drops" rather than dry test strips) have a shelf life.
Question: Why did my pool turn green after shocking?
Answer: This is a chemistry issue. If the pool turned green immediately after shocking the pool, then there is an imbalance with other chemicals or something else has been added to the water that should not have. If the pool has been brushed and shocked, it will take a few days to filter out the "green" and for water clarity to improve. If the pool has been shocked and is no longer green, but turns green again after a day or two, check the water chemistry and pay particular attention to phosphates in the water. Clean the filter often during this process. After shocking the pool, filtration becomes a key factor in clearing up a pool.
Question: I have an above ground Hayward sand filter. Does it have a vacuum to waste system?
Answer: If it has a multi-port valve that has a "waste" position, then yes. If it is a plunger type backwash valve, then no. Hayward systems, like other brands, vary depending on the model.
Rob Hampton (author) from Port Richey, Florida on July 17, 2020:
Hi Gary. Sounds like stabilizer is way too high, you could be experiencing chlorine lock. Also check for high phosphates.
Gary W Keelin on July 16, 2020:
I have an above ground pool. It's been green ever since we received a major rain storm. The chlorine level is 10, PH 7.2, stabilizer 150. I have shocked and nothing. I have also back flushed several time, with a sand filter. Ideas please!
Rob Hampton (author) from Port Richey, Florida on June 13, 2019:
Moore70813, I would look into testing phosphate levels. If it's a commercial pool, probably uses a "vac-pac" system or a tank with the grids in it. Make sure there is plenty of flow and the pre-coating of grids is done correctly. When you shock the pool, use some sodium bromide as an algeacide.
Moore70813 on June 13, 2019:
Im a maintenance man overseeing a 25 000 gal pool. High traffic pool at apartment complex. Im shocking and clorinating but pool turns green within 1 day of clearing pkease help
Rob Hampton (author) from Port Richey, Florida on May 14, 2019:
Hi Dennis. I don't fully understand your question but I would suggest that you make sure your chemicals are balanced and the filter is clean.
Dennis on May 14, 2019:
I stayed a month without treating a pool because there wasn't chemicals but they had supplied me with Chemicals I've started treatment this is now the second week but there is just a slight change,what should I do?
Rob Hampton (author) from Port Richey, Florida on May 08, 2019:
Hi Tony, thanks for reading. I'm a bit baffled on this one. Could the manifold be cracked? One thing to try would be to backwash the filter, add fresh DE powder and see if any of the powder blows back into the pool. If it does, it means there is still an issue with the filter. (Torn grids, cracked manifold)
Tony on May 08, 2019:
Question, I cleaned the DE filters myself for the first time. Put everything back together Runned the filter for 6-8 hours the pool looked great. The following day I turned on the pump and the first 30 seconds of a green sludge came from the pool filter, after a bit it was gone. Following day did the same thing and again green sludge came out to my clean pool, but then it was gone why? Is one of the filters damaged?
Would appreciate your advice. Jo
Donovan on November 25, 2018:
I did as you said. Got up this morning and all the debris was lying at the bottom of the pool. I will vacuum when i return from work today. Just need to find a way to filter. Will definitely have to call in a professional. Thanks for the advice.
Rob Hampton (author) from Port Richey, Florida on November 25, 2018:
Hi Donovan. Thanks for reading. I am a little puzzled as to why they would advise you to drop chlorine to zero. It also sounds like your local pool shop is no different than many of the large chain pool stores here in the US. They are sales driven and will make sure to sell you whatever they can. I am guessing also that your pool is equipped with a salt chlorine generator? If anything, I would add enough liquid chlorine to bring the level up at least a little bit. Filtration will be the key to clearing up the cloudy water. Clean the cartridge often. If all else fails, you can use a floccing agent which binds the particles in the water together and then drops everything to the bottom of the pool leaving the water clear but with debris on the bottom. This method requires the ability to be able to vacuum to waste. The filter will not catch this and most of the sediment will shoot back into the pool when vacumming. If you can bypass the filter and vacuum to waste, this solution works well. Hope this helped.
Donovan Mackier on November 25, 2018:
I have been to the local pool shop. They advised me to lower the chlorine level to zero and gave me pool magnet and ph increaser to add to my pool. I shocked the pool but still my water is light green and very cloudy. I use a catridge filter a bought a new one last month. The ph is 7.2, chlorine is 0. I also have a chlorinator which they adviced i must switch off. I also added salt before the summer actually started in South Africa. Please advise because i have been struggling to get my pool crystal clear for a month now. I also added water clarifier. To be honest it seemed like they did not know what to give me to solve the problem and i have spend almost R1000 at that shop. They just give me something else when i visit the shop.
Rob Hampton (author) from Port Richey, Florida on September 17, 2018:
Hi Margaret. Higher pH will not clear up a Green pool. Although it's good to have balanced chemistry, there is probably something else going on. It's difficult for me to say without seeing everything so I can only make some suggestions. Filtration: make sure the filter is clean and with your water being green, you will need to clean or backwash the filter often...make sure there is plenty of flow and circulation. Have the water tested for phosphates. If present, you'll need to add phosphate remover. Without knowing the setup and type of pump/filter system (which makes a difference for treating a green pool) this is all I can suggest for now. Hope this helped.
margaret holmes on September 16, 2018:
the pool is saying there is to much clorine and not much ph so we put ph plus in and it is still green
Rob Hampton (author) from Port Richey, Florida on September 09, 2018:
Hi Ron. Since you have a sand filter I'm going to guess it has a multiport valve that allows you to drain to waste? If so, use a floccing agent, drop everything to the bottom and then vacuum out to waste. You'll lose a couple inches of water, but will be worth it.
RonC on September 09, 2018:
I applied recommended chemicals from a local pool store, followed their processes with a powder to start, then 6 pouches of a super shock that were applied over a recommended time period. While this has worked in the past, I have seen absolutely no change in the water this time. I have a 12,000 gallon in ground with a sand filter. Any thoughts?
Chelsey on August 30, 2018:
Thanks for the advice. I went yesterday had had my water tested again but for phosphates. They were through the roof! I treated for them yesterday and this morning I can see the bottom of my pool! Need to carefully vacuum but I might be on my way to a clear pool!
Rob Hampton (author) from Port Richey, Florida on August 29, 2018:
Chelsey, when vacuuming to waste, you will lose a few inches of water. Sometimes though, in all honesy with above ground pools, it really is best to just start over.
Chelsey on August 29, 2018:
Thanks rob. My ph is 7.2 and I am cleaning my filter 1-3 times a day just to keep it clean and yesterday I added 4 gallons of liquid shock (pool place was closed and couldn’t find the lb packs anywhere else). Today it is much lighter in color and very cloudy. Still can’t see to the floor.
If I vacuum to waste I will have to order water (we have a well so I can’t fill from home) so I would prefer not to do that but I’m wondering if my only option is to drain it and start over.
Rob Hampton (author) from Port Richey, Florida on August 28, 2018:
Hi Chelsey. Sorry you're having an issue. As some of my customers tell me "I wish I could just bulldoze this damn pool and fill it with dirt!" lol so I understand the frustration. Make sure you have good filtration. This is nearly as important as chemicals. When it comes to a green pool, I normally add much more than is recommended or as we say in pool industry "nuke it". I would certainly add double the shock they recommended, minus the algeacide. Keep the pH low (7.2 - 7.4) run the pump as often as possible and clean the filter daily until the pool is clear. I have another article about using a floccing agent which may help you only if your system allows you to vacuum to waste. Also did they check for phosphates when testing? Hope I helped some. Thanks for reading.. Rob
Chelsey on August 28, 2018:
I have a 24ft round above ground. Currently the biggest headache in my life. Yesterday I took a water sample to a local pool place and she said my water chemistry looked good but my chlorine was basically nonexistent (which I figured since my pool is green). So I bought the recommended 2 bags of shock with algae crystals in it and added to my pool yesterday. Today almost 24 hours later, no change. Someone please help! I have been fighting my water for over a month.
R. Lindsey Parsons on August 22, 2018:
The amount of shock packets (5) you recommend is for what size pool? Ours is 25,000 gallons.
Rob Hampton (author) from Port Richey, Florida on July 30, 2018:
Eileen Rose.. Thank you for your comment. I, too hope your water stays clean and clear. Sounds like you have it under good control..(DE filter...YES!) always satisfying to hear. Enjoy your pool!
Eileen Rose on July 30, 2018:
Excellent information. Especially about our DE filter. We have a big 34X18 oval and have had issues. Hope to see clear water the rest of the summer. Thank you
Rob Hampton (author) from Port Richey, Florida on May 17, 2014:
Johng743 thank you for your comment, but not quite sure what you mean.
Johng743 on May 17, 2014:
You are my inspiration , I have few web logs and very sporadically run out from to brand. geeceddagkdf
BarneyBM on September 18, 2013:
I totally agree with robhampton, empty your pool, clean it and fill it with fresh water. I read an article of a person cleaning his son's pool, took him almost a month and liters (a lot!) of bleach, anti algae and who knows what (oh and not to mention the bottles of wine he consumed waiting for the pool to turn from green to blue). I will never swim in that pool, it will kill me!
Rob Hampton (author) from Port Richey, Florida on July 15, 2013:
@Traceylee...If you use well water, first you need to be sure the pool water is free of metals. Well water has a high concentration of certain metals. .. Iron, Copper, Magnesium, Chromium, lead, etc.. It can be devastating if you shock a pool with high amounts of metals. There are products you can purchase to rid the pool of metallic content. I've actually turned a pool black (the actual finish turned black) in my younger days by shocking it without testing the metal content. Luckily I was able to fix it with citric acid. Just get a quart or two of metal remover before shocking, circulate for 24 hrs, you'll be fine
Traceylee on July 15, 2013:
What if you used well water in your pool and shocking or adding chlorine makes it turn green...or brown depending how much shock was used..
Rob Hampton (author) from Port Richey, Florida on June 17, 2013:
@Michele..Thanks for inquiring. Sounds like a drain/clean and acid wash to me. If you have anything other than a DE filter, then you will need to drain the pool. The cost of re-filling a pool is not as costly as most people would assume, so don't let that scare you. Less than $100.00 for sure (unless you have some crazy Olympic sized pool) If you have a DE filter, it can be cleaned chemically. let me know if you have any questions at all. I can walk you through both the drain/clean process as well as a chemical clean. Just shoot me an email. Good luck...Rob. . . email@example.com
Michele on June 17, 2013:
We had some eletrical issues and our pool pump was down for 2 weeks. We live in Florida and between the heat and rain our pool is now black. I put 2 shock treaments in it, but that did nothing. Was going to go get chlorine to put in pool. Should we drain or can we treat to get blue again? Thanks for your help!
Clayhounds on June 09, 2013:
Nicely written Hub. Also like all the links. By the way, I do have a swamp pool that I will try these steps
Rob Hampton (author) from Port Richey, Florida on May 21, 2013:
Dr alex murray.... That is one of the weirdest comments I have ever seen. Sounds like you are counterfeit money maker? Hopefully the feds will give you a call.
Rob Hampton (author) from Port Richey, Florida on March 21, 2013:
Cheryl, I hope it helped, thanks for the comment. I'll be sure to check out your site. Rob
swimfan from United States on January 08, 2013:
Awesome step-by-step guide. Seems like this is an issue that plagues a lot of pool owners.
Rob Hampton (author) from Port Richey, Florida on July 30, 2012:
I suggest highly that you drain and refill. It would cost far less than spending money at those pool stores that try to sell you stuff you don't need. The other alternative is a flocking agent, or "drop out" or "drop and vac" This will sink all of the algae to the bottom of the pool and will need to be vacuumed out to waste. Does your sand filter have a multi-port valve in order to vac to waste? I would consider installing a cartridge filter as well. Will save you a lot of headaches.
Pixtaker on July 29, 2012:
what do I do about an above ground pool that has the same problem? We've sunk at least $300 at the pool store.....it was clear for 2 weeks, then slowly returned to this pea soup state even while maintaining....we have a sand filter and i can see the top stair almost the second....
Rob Hampton (author) from Port Richey, Florida on June 09, 2012:
Johnr54, Thank you for your comment. Battle is a good word for that. I know how difficult cleaning up a pool can be sometimes. Glad to hear you finally have it taken care of. Feel free to post any questions you might have in the future.
Joanie Ruppel from Texas on June 09, 2012:
Very useful hub. I am a widow taking care of a big pool that we use often. I use a pool company to maintain the pool, but am happy to read more about what to do for a green pool. I am happy to say we are crystal clear after 6 weeks of battling the green!
Richard Stephen on August 10, 2010:
I've had to go through this process a couple of years ago. Your instructions are basically what I did too. The improvement after 24 hours was amazing and the pool looked great after 3 to 4 days. It is important to clean the cartridge filters (if you have them) as the algae will clog them and make your pump work too hard. After a few days of filtering, a clarifier will help clear up the cloudiness. Good hub!
Karen Reader on June 01, 2010:
From green to clean, I like that! These are some great tips on taking care of your pool. Thanks for sharing.
Pool Chemicals on May 12, 2010:
Great hub. Breaking this down into steps definitely makes it easier to understand. Thanks for sharing.