My pool turned green AFTER adding chlorine. Why is that?

I've noticed this a lot on estimates. So much so it's probably the most puzzling thing to people. They are perplexed why their pool turns green after adding a bunch of chlorine to the water. I'll touch on a few reasons for why this happens. In fact the featured photo is a client's pool that had this same issue. He was at his whit's end because he didn't understand it.

High PH: Chlorine works better at a lower PH. The recommended PH level is between 7.2-7.8 with 7.5 being ideal. Chlorine works more effectively at 7.2 than it does at 7.8 even though a PH at either of those two are considered acceptable. So when your pool's PH is at 8.0, 8.2 and above it's not working as efficiently. This would rarely be the reason why your pool would turn green but it certainly is a contributing factor.

Filter Run-time: If you pool is not turning the water over at least once a day then it could lead to your water turning green. We really need all of the water to cycle through the filter daily to clean it in order to rid the water of contaminants. This holds true especially in the summertime. Generally speaking we need the filter to be running 8-10 hours a day during the summer time mainly because to the higher temperatures and higher bathing loads. Both are responsible for eating up your available chlorine which can turn into a green pool. In the winter time you can get a way with 4-6 hours. So make sure you have your pool system running adequately each day.

Not Enough Chlorine: I know this seems laughable but it does happen. I took over a client who's previous company stated they had a 8,000 gallon pool. After I measured it out it actually was 14,000 gallons, nearly double. So it was impossible for them to put enough chlorine in the water for their sized pool because they were dosing for something nearly twice as small. So make sure you're putting enough chlorine in your water to keep it clear!

Too High Cyanuric Acid Level: This is probably the NUMBER ONE reason people have green pools after adding chlorine. In fact, this exact situation happened with 2 newly acquired accounts that we are fixing this weekend. Cyanuric Acid (stabilizer, conditioner, CYA) is essentially sunblock for chlorine. Too little of CYA and the chlorine burns off pretty quickly which can lead to a green pool. However, too much of it and it basically turns into handcuffs for chlorine and not allow it to work properly in sanitizing your water. The recommended range is 30-50ppm. If you're approaching 100 or even more it's time to correct it. The only way to reduce CYA is through water replacement which means a partial drain and refill. There is a specific relationship between CYA and chlorine. Optimally, your chlorine should be 7.5% of your CYA reading. So, if your CYA is 110ppm that means you need to keep your chlorine at a minimum of 8ppm to keep that relationship held true. That is double of of the recommended chlorine levels of 1-4ppm. See where I'm going with this? If you kept your chlorine at 4ppm you'll get a green pool.

How does CYA get too high? Well there are two types of chlorine; stabilized and un-stabilized. Un-stabilized is liquid chlorine. Stabilized is the trichlor pucks (3" tablets) or granular dichlor. The stabilized chlorine has CYA in it. So when you're shocking your water or putting an endless supply of hockey pucks in your pool you're adding CYA to the water and may not even be aware of it. Overtime, you will run into this situation because the stabilizer is too high. So just be aware of what you're putting in your water. I'm a big advocate for liquid chlorine because you are not adding CYA when you sanitize your water. Stabilized chlorine is great for certain applications, but your standard liquid chlorine is the best for daily/weekly sanitizing.

So there you have it. That's not all of the reasons why but certainly some more of the main culprits of green water after adding chlorine.

Clear Up Your Water NOW!

27 Responses

  1. Laura
    I'm so glad I came across this. I'm a new pool owner and have never heard of CYA. I tested for it and it was well over 100. What do I need to do? Thanks. Laura
    • Laura what I would recommend is doing a partial water replacement (drain and refill). It really is the only option as there is not a chemical to reduce CYA. Companies have tried but have not had any luck. Do you have the exact CYA number? With the recommended range being 30-50ppm I would do a little math to figure out a ballpark for how much water you need to drain. For instance, say your CYA was at 150ppm, for easy math. So divide your pool into 3 equal parts and you'll see that you need to drain a minimum of 2/3 of your pool to get your CYA in range (albeit on the high side). From there, fill it with fresh water and balance the other chemicals and you should be good to go! Also watch the stabilized chlorine you put in so it doesn't get out of control again! I hope this helps!
  2. I have a 2,500 gallon Index that was just put up and filled yesterday. The water was perfectly clear until about an hour after adding chlorine. Now the water is sort of pale green. I do not know the CYA level but emptying and refilling would be useless due to the fact that I'd be filling with the same water. Also I can't refill due to being on a well and right now I cannot afford to get another water delivery.
    • Hey Kari, are you using well water by chance? It sounds like you had a reaction from adding chlorine to water with high metals in it. If you're using well water, use a metal treatment (Jack's Magic) and then something like CULator metal remover to remove the metals out of the water. That should solve your problem.
  3. Most of the reasons in this article are for a pool that is green when chlorine is expected to be adequate. Not why it "turns green right after adding chlorine. I've been a CPO for 20 years, but was just surprised that my pool turned green after adding 1lb dichlor, 1lb cal hypo. Its winter in GA water temp is in the 50's. We've had some heavy rains over the past 3 months and I was not too concerned with the pool water. It was clear, not green, and otherwise clean. I'm sure the chlorine was zero. It wasn't "sparkling", so I decided to add some Cl. I added 1 bag of dichlor (and one cal hypo) as I knew the recent rains had diluted my stabilizer (its now at 30ppm CYA and chlorine is now 5ppm). But within a couple hours after adding these yesterday it turned olive green! Profoundly different. Its my own pool that I've managed for 4 years. The symptoms suggest copper, but I don't know where Cu could have come from. I have not added any well water (probably in a year) and I've never added any algaecides. nor had any metal issues on this pool or another pool on a well 3 miles away that I've managed for 20 years. I don't have a cu test yet. Its puzzling and I'm torn between shocking it outright or checking for metals. Suggestions?
    • Thanks for the post. I'm assuming the green that it turned is a clear green? You're right, that does suggest copper. You said that you haven't added well water (in about a year) but the water you did add could have put some copper in there. Then when you spiked the chlorine up it oxidized the copper. What was your pH prior to shocking the pool? A higher PH will cause things to start falling out of solution, like copper for instance.
  4. Our pool is green we add 2 gallon of pool sanitize yesterday and our pool is still not cleaned up we have a 24 × 52 how much chlorine should we be added please help
    • I would add much more than that. I would add at least 5 gallons. The goal is to turn the pool a cloudy blue/white and then you have enough chlorine in it. If you don't hit it hard enough it'll just grow back. If you have a vinyl or fiberglass pool go a little lighter on the chemicals to not cause surface damage. Good luck!
  5. Hi I have a bestway 2300 litres been adding 1 tab into the pool for a week and it’s turned green what should I do
    • Please tell me your other readings and the size of your pool. How old/type is your equipment?
  6. My husband is going crazy. We had our pool water tested, and yes it was high on CYA. We drained our pool like it was suggested. Filled it back up. We have well water. Did all the steps the company told us to do. Tested the water again. A little better but still very high and not taking chlorine. Drained and refilled again. Today my husband put granular chlorine in the pool, and now it turned green. I read some of your responses to other people. Is it because we have well water? Is it because we use granular? We are at wits end. We hope to have this pool right by July 4. Please help
    • Hey there! Is it a transparent green? It sounds like the shock oxidized the metals in the well water, causing this reaction. Please get back to me on how clear the green is.
  7. Hi! We have a 15 x 48 Intex metal frame pool. It recently had an algae bloom while we’re we’re away (don’t think the neighbors ran the filter pump for us). The 1000 GPH filter pump is terrible and we’re awaiting the arrival of a 2500 GPH one. In the meantime, I shocked the pool using a bag from the pool supply, probably about 1 lb. I cleared and cleaned the pool of any physical algae I could see but now it’s a cloudy green color. I’m thinking this is do to the poor filter pump, which we’ve kept running constantly and have also been cleaning daily. Wondering if you have any other thoughts or recommendations? I’m really hoping it’s just the weak filter pump not turning over the pool water fast enough. Appreciate any feedback or suggestions. Thanks so much!
    • What type of filter do you have? There's three ways to get a green pool. 1) Bad Chemistry, 2) Bad Circulation, 3) a combination of the three. It sounds like you didn't put enough shock in. Once the pool turns a cloudy white/blue then all the algae is dead. Keep the free chlorine high, keep the filter clean, and keep the system running. It'll clear up. Here is a video I did on my YouTube channel about green pools. I hope this helps!
  8. Help!!! My pool is green. Ph level is good. Chlorine level is high. I partially drained and refilled. We had some floating light balls and one was filling with water. Not suppose to happen. So if water got inside ball that means water from ball got in pool. Could that be???
  9. Hi! I have a glorified kiddie pool! It’s one of those Intex 1000 gallon pools. Chlorine levels are too high according to a read yesterday, but the pool is still a foggy green. Last week it was just cloudy but not green. Chlorine levels were high, alkalinity was low. So I added baking soda which cleared things up, but now it’s green. Any suggestions? Thanks much!
    • Thanks for the question Jon. How long is your system running for and have you done a phosphate test? It sounds like a phosphate issue to me.
      • Thank you! System not running long enough apparently! I haven’t done a phosphate test. I’ll do that next. Should I just go ahead and treat the phosphate problem assumptively or is it important to wait for the test results? Thanks!
  10. Hi there, I have an intex frame pool. 14' x 42". Used it for around a week before i did a ph and chlorine level test and the pH seemed good at 7.6 but the chlorine level was zero as I have not previously added chlorine before. Using my recommended amount I should put in 5 chlorine tablets into a floater which I did. After about 5 minutes water started to turn greenish. Unsure as to why this has happened please help.
  11. We have a new Intex 32x16x52, saltwater pool. When we filled the pool, added the requisite amount of CYA and salt (on a very hot day) and ran the filter 24 hours, we noticed the chlorine levels were barely registering. We didn't like the location of the pool, drained it and moved it to another location. The set up was like the first with the same outcome relative to chlorine levels (also VERY hot days. Over 100 degrees) so I shocked it while running the filter. Within about 3 hours it turn light green. Test kit shows pH at 7.4 but cl in the 5-10 range. I am thinking it's cooper in the water. We don't have well water, but the water is hard. I'm still running the filter. Thoughts, ideas, solutions?
  12. Pool was not filtered and was without chlorine for a week resulting in an algae bloom. Shocked the pool and it mostly cleared but was still cloudy. Shocked it again and it is now cloudy and green again! What should I do?
  13. Pool was not filtered and was without chlorine for a week resulting in an algae bloom. Shocked the pool and it mostly cleared but was still cloudy. Shocked it again and it is now cloudy and green again! What should I do?
  14. Help! filled my intex 1700 gal. with rain and well water. Was crystal clear. Added appropriate amount of powder cholorine, now almost immediately olive green. Not cloudy, just discolored. I read this is because of metal? I don't want to go buy a bunch more chemicals for this size pool. Did not have this problem last year. Should I just drain some and start over? Any chance it will clear up on own?
    • Hey Molly, it sounds like the powder chlorine oxidized the metals that came from your well water. You could drain and start over with only city water, but if you have only well water I'd skip draining. Add some metal sequestering product and a metal remover like CU Later. That should help eliminate the metals from you water so the copper doesn't show up next time you add chlorine. Hope this helps.

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