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Thread: Water turns green after adding chlorine

  1. #1

    Water turns green after adding chlorine

    Hi all ... I have been doing BBB for several years now with great success. This is the first year I've run into this kind of problem and am seeking a little help. My pool water is crystal clear, but when I add bleach (using the regular household 6% variety) my water turns a nice shade of green -- well, more like green-blue.

    Here are my most recent test results:

    FC 3
    CC 0.5
    CH 200
    CYA 60
    TA 100
    PH 7.4

    I ran a sample to the pool store to test for metals, because I don't currently have those test kits available. Anyway, my copper and iron levels were 0. Total dissolved solids (whatever that means) came out to 1100. Phosphates were 300 (high according to the pool store), but I understand that test doesn't really mean a whole lot, if I am not mistaken.

    I was doing some searching on the forums, and I saw one post that suggested pool store tests for metals are not very accurate. I also saw a suggestion that these types of situations require the use of a sequestrant. I have NO idea what that is. This is where I am seeking the most help, I think.

    I also discovered a few days ago that the metal ring around my pool light looks a bit corroded. Perhaps rust? I haven't been able to get underwater to fully investigate, but I am wondering if this is culprit for the green water. My husband said the metal ring is too small to make a significant change like that, but I am not so sure. We also had a slight accident in the spring when some of the rain water from the top of the cover spilled over and mixed in with the pool water. Don't know if that means anything, but I'm throwing that out there, too.

    So, where does this leave me? I have to say the water is beautifully clear, but this off coloring is really bothering me. I'm a little hesitant to get in until I know what's causing this. Thoughts?

    (As an aside I mistakenly told the guy at the pool store that I use bleach and he said that was why my pool was turning green! All those "fillers" in the bleach cause that, he said. Ha, I know, right?)

  2. #2
    Mod Squad zea3's Avatar
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    Re: Water turns green after adding chlorine

    Do you use well water? If you use city water look on their website for info on water quality and see what it lists for metals. Also did you use an algecide that contains copper to close or start up? Clear green water is usually a sign of copper in the pool. You can try adding a sequesterant such as Jack's Magic to see if that clears things up.
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  3. #3
    Administrator JasonLion's Avatar
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    Re: Water turns green after adding chlorine

    ProTeam's Metal Magic and Jack's Magic the Pink Stuff (regular), the Blue Stuff (fresh plaster), and the Purple Stuff (SWG) are some of the top sequestrants. You can also find many other brands with similar ingredients, some of which are noticeably less expensive. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are the most effective.

    While the water is green the metals are in the form of micro-crystals, which will not show up on the test because they are not dissolved.

    Lowering the PH is a way to clear the color temporarily, but it will come back if that is all you do.
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  4. #4

    Re: Water turns green after adding chlorine

    I use city water -- will go and see what information I can find, thanks! I've been using city water to fill my pool for years, though, so I am scratching my head that I suddenly have this problem. (About half of it gets drained every year when we close, and then filled with fresh in the spring.)

    As far as sequestrants, what do they actually do? Does it clump the tiny particles, which helps it filter out better? How much of this do I need to use and how often? Is it a one-time thing, or will I need to get several bottles and add it over time?

    Glad to know I am on the right track anyway, I think! Thanks for the replies!

  5. #5

    Re: Water turns green after adding chlorine

    Oh, I forgot to add, I think we might have added some algecide at the end of the year, but it is the Pooltrine 60 brand. (Polyethylene dichloride) I don't believe it has copper in it.

  6. #6
    Mod Squad zea3's Avatar
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    Re: Water turns green after adding chlorine

    Do you have any copper piping for the pool or a heater with a copper heat exchanger?
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  7. #7

    Re: Water turns green after adding chlorine

    No heater, and I believe all of my piping is PVC. Well, at least everything I can see is. Not sure what's underground, but I am sure it is pvc, too.

    I am going back to the light fixture that is corroded. You guys think that might be the culprit?

  8. #8
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    Re: Water turns green after adding chlorine

    You guys think that might be the culprit?
    No. I have had the same condition in my pool for the last three start-ups each Spring. It goes away after a few weeks and doesn't reappear the rest of the swim season, regardless of the FC level.

    To me, it is unexplained. Like you, I have used the same water source for 5 years prior to this with no surprises. Something is obviously precipitating out of the pool water when chlorine is introduced but my pool tests ZERO for both Iron and copper both before the green and after the green. I remain puzzled but I do believe yours will be transient and will go away even if you do nothing, if it's the same issue I have had.
    Dave S.
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  9. #9
    Administrator JasonLion's Avatar
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    Re: Water turns green after adding chlorine

    Sequestrant binds to the metals in the water and prevents them from depositing as stains or coloring the water. The metals remain in the water, and eventually the sequestrant breaks down, so you need to add more occasionally.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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