Rob is a pool-service industry professional with over 20 years of experience.
Green Pool Water
Judging from the questions pool owners ask on the internet, they are having a hard time with water clarity even when they think all the chemicals are balanced. We will discuss in this article why chlorine, pH, and alkalinity are only the beginning in maintaining clear pool water, and then we will troubleshoot the problem.
Basic Chemical Requirements for Clear Pool Water
Just to summarize, these are three basic chemical requirements for a pool that stays clear.
- Free chlorine: Unless the water has a sufficient free chlorine level, algae will grow and make your pool green and cloudy.
- Correct pH: For normal use, your pool’s pH should be between 7.4 and 7.6: for shocking, it should be between 7.2 and 7.6. Shocking a pool with too high pH will cause cloudiness.
- Correct alkalinity: The right range of alkalinity (dissolved salts that keep pH stable) makes pH and chlorine levels easier to maintain.
5 Green Pool Questions
- I Shocked my pool, so why is it still cloudy? Still Cloudy?
- I shocked my pool, so why is it still green?
- How much shock should I add to the pool? Did I add enough?
- Will the pool turn green if I don't add chlorine?
- How long should I run the pool pump? Am I filtering my pool enough?
1. I Shocked My Pool, so Why Is It Still Cloudy?
If your pH is not too high, filtration issues are likely the cause of your cloudy pool. The issue may depend on the type of filter.
- If you have a sand filter, it could take a week or more for the pool to completely clear. That's even if it's a working sand filter.
- If you have a cartridge filter, it needs to have a good cartridge. A cartridge can only handle so much. If your pool is cloudy, the cartridge needs to be cleaned DAILY until the pool is clear.
- If you have a diatomaceous-earth (DE) filter and the pool is cloudy, then
- Either the pump is not being run on a long enough cycle
- The DE is not fresh because it’s not being backwashed
- Or the filter is defective and not working properly. (Do you have torn filter grids? A broken manifold? Does DE powder shoot back into the pool when you add it? If so, the filter needs to be taken apart and cleaned or repaired, and your pool will remain cloudy until the repair is made.)
So remember, a cloudy pool can be caused by a bad filter.
If the pool is being filtered properly, you won't need a clarifier solution. In some cases, you can use a flocking agent, a product called "drop out" or "drop and vac," that will bind small particles together and sink all of the algae to the bottom of the pool, where it can be vacuumed up as waste.
2. I Shocked My Pool, so Why Is It Still Green?
This is one of the most often searched questions. High levels of the wrong chemicals may be the issue. Let's take a look at reasons why your pool may still be green even after you've exhausted yourself by adding tons of chemicals.
Over time, if you use tablets (like Tri-Chlor) to supply chlorine, levels of the stabilizer from the tablets (cyanuric acid) can become elevated and “lock up” the free chlorine molecules (Cl2). Even if you get very high chlorine reading on your test kit, the chlorine is simply not able to work at killing algae because it’s not in the right chemical form. This article shows you how to lower stabilizer levels.
High phosphate levels can definitely cause algae problems. Phosphorus, or phosphate, can enter the pool by leaching out of leaves or organic debris in the pool or drifting there from fertilizer sprayed near or around your pool. Because algae feed on phosphates, algae blooms due to phosphorus can become overwhelming in the summer months when the water temperature exceeds 78–82° F. This condition is easily treatable with a phosphate-removing product like this one.
3. How Much Shock Should I Add to the Pool? Did I Add Enough?
"Shocking," a pool that has turned green, is better known in the industry as "super-chlorination."
When shocking the pool, consider a few factors. How big is the pool? How "green" is it? If your pool is a normal residential-sized pool of 13,000-25,000 gallons (the pool pictured at the top of the article is around 18,000 gallons), then your options are liquid chlorine or granular shock. The choice depends on what type of filter it has.
- If it is a sand or cartridge filter, I will use liquid chlorine, about 10 gallons, or four of the yellow "Jerry-jugs." I use liquid chlorine because granular chlorine will leave a residue that is harder to filter out.
- If the pool has a DE filter, then I will use granular chlorine (about 5 pounds). This article shows how I shock a pool with a DE filter. Remember to test the water before adding shock. The pH should ideally be low when shocking the pool (around 7.2) because shocking the pool will raise the pH level.
Remember that shocking alone does not clear up a green or cloudy pool; that is what the filter is for. It doesn't matter how much shock you put in the pool if you have a bad filter.
4. Will the Pool Turn Green if I Don't Add Chlorine?
Believe it or not, I have seen this keyword search pop up more than once. There is a short answer: YES, IT WILL turn green if you don't add chlorine. Pool water must have a sanitizer or something that will kill bacteria and algae. Algaecide alone without chlorine will not prevent the pool from turning green.
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5. How Long Should I Run the Pool Pump? Am I Filtering My Pool Enough?
Always run the pump when shocking the pool and allow it to circulate for 24 hours. The water should then be a blue or cloudy blue color.
Test the water 24 hours after shocking and start adjusting pH and alkalinity levels. The chlorine will still be elevated, but over a few days, it should stabilize. You could add sodium thiosulfate to lower the chlorine level, but I do not recommend this because adding too much can cause the chlorine level to seesaw back and forth.
After the shocking process is complete and you are back to normal operation, you need to set your timer, so the pool is filtered for a long enough time each day to deal with any algae or debris. How long to run the pump depends on the turnover rate: the time it takes for the circulation system to move the entire volume of water in the pool (the number of gallons) through the filter equipment.
During the hot summer months, an average-size residential pool that is in use should be filtered for a minimum of eight hours. During the cold season (since algae grow slowly in cold water), or when no one is using the pool, the filter time can be cut in half. But the pool water does need to be filtered whether it is being used or not.
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 put the hth Super Shock green to blue 1 in my above-ground pool, and now it's light green. What should do I do next?
Answer: After shocking the pool, it will need filtration and circulation. Run the pump as much as possible. Keep the filter clean (daily) until the water runs clear. Be sure to brush the pool often during this process as above-ground pools do not have drains at the bottom. A clarifier solution can also be used to help out.
Question: How long do I backwash the sand filter of my pool?
Answer: Sand filters require a longer backwash time than a DE filter. Both work by reversing the flow and blowing buildup and debris to waste (or backwash hose) In my personal experience with sand filters, a solid 2 minutes is sufficient. I have heard that backwashing a sand filter for 5 minutes is good. Unfortunately, you'll lose several inches of water if it's backwashed that long. So, a good tip would be (and this is what I do for sand filters). Backwash for 90 seconds. Bring valve back to filter position and run for one minute. Backwash again for another 60 seconds. Should be good to go after that. If you have a "multi-port" valve then there should be a rinse cycle. Run the rinse for 30 seconds after following the above steps.
Question: My pool is green. The alkalinity is 180 and the pH is 6.8. What can I do to make it clear?
Answer: Balancing the chemistry will be the first step. Start with chlorine, pH, and alkalinity. Without knowing the volume (gallon size) of the pool, I can not answer this accurately. Please try this pool chemical calculator for adjustment and dosage amounts.
After chemicals are balanced, filtration will be the most important factor in clearing the water. Run the pump as often as possible, cleaning the filter every 2 days until pool is clear
Question: I have an above ground 24 x 52 round pool. I have cleaned the pool and started with clean water. We have rust in our water. I have put 32 ounces of algaecide along with 4 shocks, and 5 bottles of chlorine. The water is green. I have a sand filter with brand new sand. What can I do?
Answer: Above ground pools can be difficult when trying to get rid of algae, only because there is no "Main drain" or a drain at the bottom of the pool which helps the filtration process greatly. An above ground pool usually only has a surface skimmer. If you've started with clean water, small amounts of chlorine should be added while filling. As far as rust being in the water, you need a metal sequestering agent which will remove the metal from the water. There are a couple of different ways to address the "green" in the pool. Since you have a sand filter, there should be a backwash mode in which the water is pumped to waste. Ideally, if your filter is equipped with a "multi-port" valve, then there should also be a "waste" setting on the valve. Brush the pool, add a floccing agent (this will drop all algae to the bottom of the pool) and then vacuum everything that has dropped to the bottom out to waste. Another option would be to brush the pool often and run the filter as much as possible. Unfortunately, sand filters have a higher micron count and take much longer to clear a green pool, especially if there is no main drain. The water would need to be continuously stirred up to be able to filter it through the surface skimmer. If all else fails, drain the pool and re-fill being sure that a metal sequestering agent is added to counteract the rust in the water.
Question: I used the "Green to Blue" product and the next day the pool water was clear, but I see green in the middle of the pool on the bottom. I tried to clean it, but then the pool is all green again. Do you have any advice?
Answer: So what has happened is the dead algae sank to the bottom. If you vacuumed, the filter would not catch everything, so a lot of it shot back into the pool. When adding a floccing agent, allow everything to settle to the bottom. It will then need to be vacuumed to waste. Hopefully, your filter system has a waste valve otherwise you will continue to just recirculate green water.
Question: After shocking an above ground pool with almost 16000 gallons, how long before I can add clarity solution to pool?
Answer: Clarifier can be added immediately after shocking the pool. Be sure to clean the filter daily until the pool is clear.
Question: Our pool has turned green over a short period of time. For the last two weeks, it's been about 90° with monsoon rains about every hour, every other day. Do you think the pool turned green that quick or maybe had some help from a disgruntled former employee?
Answer: During very hot weather along with progressive rainfall, it doesn't take much or very long for a pool to turn green. Without knowing what the chemical readings were the last time they were there or how well the filtration and flow is, it's difficult to say if anyone has added chlorine reducer to cause it to turn green. I would lean more toward the heat and rainfall that has caused the problem.
Question: How does too much calcium (hardness) affect pool water?
Answer: High calcium levels can cause scaling while low levels will eat at the plaster.
Question: After vacuuming the pool how long should I wait before checking chemical balance?
Answer: Vacuuming the pool will not affect the chemistry readings. It can be tested before, after or even during vacuuming and the results will be the same.
Question: Do I need to add calcium to my above ground pool?
Answer: Calcium is essential to maintain in ANY pool. Water needs calcium. If the calcium chloride level falls below 200 ppm and is not added, the water will still get the calcium that it needs by pulling it from the surface, pool liner, plumbing anywhere that calcium can be extracted from. It's important to maintain a proper calcium hardness level to prevent any scaling, staining or damage to the pool and/or pool equipment. Ideally, the calcium level should be maintained between 200-400 ppm.
Question: My husband says the water turns green as soon as we take the cover off, is this true?
Answer: No. Algae can not instantly appear or grow as soon as a pool cover is removed. It's not an "exposed to oxygen" type of thing. It was most likely already in the pool and difficult to see because of the cover. Once the cover is removed, because of light refraction, it may become more visible. When light travels from air into water, it slows down, causing it to change direction slightly. Refraction can amplify the appearance of algae when more light is available
Question: Should I run my pool sweeper if I have too much chlorine in the pool?
Answer: Running the automatic pool sweep will make no difference or have any effect whatsoever on the water chemistry.
Question: I use a cellulose fiber filter for my pool. Which is better, granular shock or liquid shock?
Answer: Cellulose fiber is used in place of DE powder. It works great, sometimes too useful since it has such a low micron count that the only thing that passes through it is water (needs to be cleaned more often). Filters out virtually everything else. If you add granular chlorine, as long as it's not added through the skimmer, will dissolve. Since sodium hypochlorite (liquid chlorine) is already dissolved, it's even better although liquid chlorine has a higher dissolved solid content. I use liquid to elevate chlorine when needed and granular if I am shocking the pool.
Question: How often do you change the sand in a sand filter?
Answer: Every 3 years is recommended unless the filtration quality begins to diminish before that.
Question: What are the “color phases” of superchlorination? I’ve been working with pool professionals and just have added 4 gallons to my 10,000 gallon above ground pool which I usually do not have too many issues with. This year I started out with pure brown and realize now I should have drained it but here I am still messing with it. It has begun to turn a more yellow light green color.... does that sound like it’s moving in the right direction?
Answer: It's good that you're using liquid chlorine for this. It will eventually turn color from the brown you started with to cloudy. The main focus should be on filtration now. If you have a small cartridge filter, you'll need to clean it daily and run the pump for an extended time each day. Also plan on buying a new cartridge because by the time the water starts to clear, that cartridge is going to be completely shot.
Question: How do you clean a sand filter in a pool?
Answer: A sand filter is cleaned by reversing the flow of water through the filter by using a diverter valve to push the gathered debris out through a waste line or hose (back-washing). If this question refers to actually changing the sand, this is done by removing the filter lid and vacuuming out the old sand with a Shop-Vac then replacing it with pool grade sand.
Question: How long after increasing the alkalinity do I wait to shock the pool?
Answer: Before shocking the pool, be sure the pH is between 7.2 and 7.6. Alkalinity should be at least 80 ppm and no higher than 120 ppm. (90 - 100 ppm is ideal) If an increase is needed, add the sodium bicarbonate or "alkalinity up", then allow the water to circulate for at least one hour and then re-test the alkalinity level. Once these levels are balanced, the pool can be shocked.
Question: The pool has algae on the walls but is clear. Why did it turn a cloudy white color right after I shocked it with two packets of shock?
Answer: In the pool industry, we refer to this as "smoking the pool". This happens when a granular shock is added while the pH is high and alkalinity is unbalanced. This can also be resolved quickly by balancing the pH and alkalinity. Before adding granular shock to the pool, be sure the pH range is between 7.2 and 7.4. The alkalinity should be 80 to 120 ppm, with 90 to 100 being ideal.
Question: Should I leave the pool cover off for 8 hrs after treating it? Or should I cover it?
Answer: The cover should be left off.
Question: How do I lower the pH of my pool?
Answer: Add pH reducer or muriatic acid.
Question: My chlorine tabs got wet, can I still use them?
Answer: Of course. They are activated by moisture.
Question: How do I determine the gallon size of my pool?
Answer: You can measure your pool by calculating length x width x average depth. You can also use a pool volume calculator. Try this one...
© 2012 Rob Hampton
Rob Hampton (author) from Port Richey, Florida on July 05, 2019:
Hi Amy. Bad filtration is normally a common cause for pools not clearing up. If you have a cartridge filter, you may want to replace the cartridge. Clean the cartridge every few days until the water clears. If you have a DE filter, might want to think about taking it apart and servicing it. This is about all the advice I can give at the moment without knowing more about what type of filter system being used
Amy Hunk on July 05, 2019:
Our pool is 40,000 gallons. I have tried all summer to get it right. Finally, all levels are perfect (ph, alkalinity...), but the water is still a real color! I take water samples to a local supply store to be tested. The chlorine level was a little high, but I had recently added shock. I’m about ready to fill this thing in with dirt! HELP! What will turn this water blue if everything is supposedly right???
Rob Hampton (author) from Port Richey, Florida on July 02, 2019:
Hi Barry. Anytime you can vacuum debris, dust or algae to waste, it's always a good thing! Thanks for reading... Rob
Barry on July 02, 2019:
I gravity vac my pool where I fill the vac hose then the end goes outside the pool to drain the waste from the pool. is this good
Leah Martin on June 26, 2019:
How do I know if my filter is bad? We have an ingound salt water pool that is about 20,000 gallons. We had some nasty storms and now our pool is black on one end and flourescent green on the shallow end. We have shocked, flocced, added anti algae treatments. Cleaned the filter and the chlorinator. Nothing is working. I am about $600.00 in the last 2 weeks on chemicals. What can we do now?? Please help!
Kent on June 12, 2019:
"Sometimes people don't like to hear this, but in this case the only advice I'm going to give is to drain pool and start over. By the time you exhaust all of your time, energy, and cost of chemicals it will be worth the cost of some water."---Yeah, I'm one of those 'sometimes people'. My wife wanted the above ground pool, and she has trouble keeping the water clear (sand filter). Last year, she filled it up 3 times, and each time filling it up is an extra $100 on the water bill. I'm really starting to hate that pool. In 2019, you'd think there would be a better answer than 'better to empty it and fill it up again'
Rob Hampton (author) from Port Richey, Florida on June 10, 2019:
Nana Dora, thanks for reading. The best course of action would be to use Soda Ash (sodium carbonate). This, unlike sodium BI-carbonate (baking soda) will raise the pH without raising alkalinity. Use small amounts until pH is around 7.4. maintain this pH and the alkalinity will eventually decrease on its own. Hope this helped.
Nana Dora on June 09, 2019:
Help PLEASE, my pool is 10500 gal, I’m having a hard time bringing PH up, and lowering my alkalinity ..... any suggestions?
Phil on June 09, 2019:
I ran into this problem several years ago. My pool was green even at ridiculously high chlorine values. The problem then was that I was using Dichlor labeled as "pool shock" which is basically stabilizer with chlorine attached. I had so much stabilizer that it was keeping the chlorine from doing anything. The only way I got rid of the problem was to drain the pool (for the first time in about 10 years). Now I only use sodium hypochlorite for shock and I haven't had the problem again. I still use trichlor for daily management which has slowly built up my stabilizer since it doesn't every really go away (even in winter).
I think the biggest reason for this being the highest googled question is the labeling of dichlor as shock. As a one-time beginning of year treatment, maybe. I would be willing to bet that most of the people suffering from the green shocked pool were doing it with dichlor. That's what all the non-pool stores (Costco, Sams, Walmart) have now and it's all labeled "shock".
Rob Hampton (author) from Port Richey, Florida on June 04, 2019:
Hi Diane. It's difficult to answer this question without knowing some things about the pool as treatment methods vary based on certain things such as..is this an in-ground, or above ground? Type of filter? (Cartridge/DE/Sand), Size of pool? (Can it be drained and refilled easily?) You could try floccing the pool. I just can't give a simple answer without knowing these things.
Diane on June 04, 2019:
We didnt cover the pool this past winter. It turned cloudy blue like milk. Been trying to clear it for two months now. The chemicals are all within normal limits. What can we do?
Rob Hampton (author) from Port Richey, Florida on June 03, 2019:
Ed, thanks for reading. You can view my article on how to floc a pool here. https://dengarden.com/swimming-pools/Cleangreenpoo...
Ed on June 03, 2019:
You need flock directions will tell you how to use
Larsen on October 22, 2018:
If chlorine is high will the water trun green coz of high chlorine
EmilyH88 on September 04, 2018:
Hi, for the first time in 20 years of owning this pool, we've struggled with cloudy water and algae all summer. We've never before had an issue managing the chemistry, and usually have crystal clear water. Have had the water tested multiple times and local pool store is out of ideas.
We brush the walls/bottom then shock, then after the water starts to clear, use a floc to settle out the remainder and vacuum to waste. But pool never completely clears, and algae starts to grow again within a week, even with high remaining chlorine (5+ ppm).
Currently (48 hours after most recent brush and shock) we have:
Stabilizer: 20 ppm
Free chlorine: 11.4 ppm
TA: 120 ppm
Calcium hardness: 190 ppm
Phosphates: 0 ppb
16,000 gallons. Sand filter running 24/7. Sand was replaced in June.
Pool is green--is the same color it was 48 hours ago when we shocked it, using liquid shock. There has been zero change.
Help? Any ideas? We're at a total loss, and so is our local pool store!
Christine on July 27, 2018:
I have a 5500 gallon pool that has had issues staying clear. we have had people fired over and still cant find the issue. we took the water to be tested and shocked it, got all new spider valves. Vacuum it and scrub it every other day. It has rained a a lot however the color started before hand. The temp is around 78, ALK varies from 60 to 80, and the PH Level is 7.4 to 7.6. chlorine has varied a lot in the last week.
Rob Hampton (author) from Port Richey, Florida on July 24, 2018:
Hi Elizabeth. It sounds like you are having the EXACT same problem as "Kim". Please read the comment I left for her. Thanks
Elizabeth on July 24, 2018:
I just opened my above ground pool (15ft round x4 ft high) and it was super green and yucky. I purchased a new pump and filter and shocked my pool Sunday night and took some water to the pool store and was told it was locked up so to shock again so I did that last night. I have had the filter running since Sunday afternoon. the pool is still green and cloudy and all levels are showing very low. I don't know what to do next? wait it out? we clean the filter 3 times a day.
Rob Hampton (author) from Port Richey, Florida on July 24, 2018:
Hi Kim. Sorry to hear the pool looks so bad. Sometimes people don't like to hear this, but in this case the only advice I'm going to give is to drain pool and start over. By the time you exhaust all of your time, energy, and cost of chemicals it will be worth the cost of some water. The filter element can only handle so much. It will need replaced soon because trying to filter it all out and cleaning it constantly is very hard on it. There is really no way of me knowing why it's not holding chlorine without being able to do a full range chemical analysis. I hope this helps.
Kim on July 24, 2018:
HELP! I am very frustrated. We have a pop up 15 x 48 pool. Just got back from a 1 week vaca and the pool was a very dark green from algae growth. I shocked it and added algae killer. Now its been 2 days and it still has some green but VERY cloudy! I am cleaning the filter cartridge 3 times a day. No cover on the pool, exposed to the sun. What am I doing wrong? How long will this take to totally clear up? Why do my test strips say there is NO chlorine in the pool (even though I've shocked and have added 6 oz of chlorine 24 hours later) and the PH is way too high even though I have added PH minus? Do the test strips even work?? Do I now have too much chlorine in it so the strips won't read it??
Reneygade on July 23, 2018:
We've tried everything that we've googled, that's applicable. Why is the pool water still green? This has been an ongoing issue for about 3 weeks now.
Rob Hampton (author) from Port Richey, Florida on July 23, 2018:
Hi Tony. Yes. It's dangerous. So many diseases in pool water that is not treated and filtered.
Tony ure on July 23, 2018:
hi is this colour water dangerous to swim in or just unpleasant because of its look? thanks
furniturez from Washington on August 08, 2012:
No wonder my neighbors pool is green! Lots of insight thanks so much.