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Thread: Pool went green overnight?

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    Pool went green overnight?

    I just got back from a 12 day vacation and found the pool in ok shape. It was not green and still had FC =4 after being at shock level when I left it so I added a bit of chlorine to get the FC up a bit. I cleaned the pool and it was looking good. The next morning I looked and the water had a green tent to it. The only thing I had done was to turn the pump off over night after the chlorine was mixed as I did not want to backwash and the flow had diminished some. I had turned on the heater get the temp up some also. Wonder why it went green? Any thoughts? And what should I do now? Take it back to shock level?
    27 foot round above ground

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    Richard320's Avatar
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    Re: Pool went green overnight?

    Quote Originally Posted by fishcrazy
    I just got back from a 12 day vacation and found the pool in ok shape. It was not green and still had FC =4 after being at shock level when I left it so I added a bit of chlorine to get the FC up a bit. I cleaned the pool and it was looking good. The next morning I looked and the water had a green tent to it. The only thing I had done was to turn the pump off over night after the chlorine was mixed as I did not want to backwash and the flow had diminished some. I had turned on the heater get the temp up some also. Wonder why it went green? Any thoughts? And what should I do now? Take it back to shock level?
    Clear green or murky green? And as always,
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    Re: Pool went green overnight?

    I can see the bottom but the water color is green and not clear. My FC is now 10 after adding bleach and CC=0. I did not check CYA but it has been 50 recently. It is a vinyl above ground 27' rnd pool. I added borax to get the Ph up some. It was 7.2 and I wanted it at 7.8. I think maybe I should shock it but thought I would see what you all think.
    27 foot round above ground

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    Re: Pool went green overnight?

    You need to shock. With a CYA of 50, shocking is adding enough bleach to get you to 20 ppm FC. 10 is only halfway there. You are finished shocking when your water is clear, your CC is 0.5 or less, and your pool loses no more than 1 ppm of FC overnight.

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    Re: Pool went green overnight?

    OK Thanks for the reply. I was afraid of thaat. Was looking forward to swimming tonight. Wonder what caused it to turn green all of a sudden.Could turning on the heat have anything to do with that.
    27 foot round above ground

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    Re: Pool went green overnight?

    Yes, I'd bet that warming up the pool sped up nascent algae growth that had already gotten started, but was not yet visible. You will never get algae to bloom like that overnight. Algae only doubles in population every 3 to 8 hours under ideal conditions so it takes at least a day for any introduced algae to begin to be enough to just barely be visible and usually it's after 2 or 3 days when it turns into a full-fledged bloom. If you see this happen faster than that, then the algae was already there just below visible threshold.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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    Re: Pool went green overnight?

    The pool looks better but still has a slight green tint to it. The FC=18 this morning. I guess I am going to put another bottle of bleach in to get it up to 20 again. I cant do an overnight test till tonight though. At whayt level of FC is it not harmful to swim in the water. I think the water looks ok to swim but the wife doesn't think so. I agree with her on the slight green tint but it is very slight to almost not noticeable. Is it dangerous in any way to swim in it with the chlorine at 20 and the green tint?
    27 foot round above ground

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    Re: Pool went green overnight?

    You can swim up to shock level. Shock level is equivalent to a pool with 0.6 ppm FC and no CYA so somewhat less than typical indoor commercial/public pools. You will likely notice the chlorine (or chloramine smell on your skin), but it's not very reactive because of the CYA in the water and you wouldn't notice anything with swimsuits for just a day or two (over months, yes, as my wife can attest from swimming in an indoor commercial pool over the winter). Of course, you don't want to drink gallons of pool water, but you wouldn't do that anyway.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Pool went green overnight?

    I just wanted to chime in om the swimming with high FC. A few weeks ago it was so hot and sunny I jumped in the pool at 30FC with 30 CYA and had no fading of orange swim trunks, no dry skin or irritation. But we also had less than 1 CC. I think when the experts here say its the CC that are irritating, smell, and fade clothes, they are correct. Your mileage may vary, but I wanted to share my experience. The pool with 30FC and 30 cya had no chlorine smell at all, but when we were first shocking the smell was pretty strong.

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    Re: Pool went green overnight?

    Wow, 30 ppm FC with 30 ppm CYA is actually a lot higher, but of course there's a lot of possible error in the CYA measurement. It's roughly equivalent to 5.4 ppm FC with no CYA so that's high.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Pool went green overnight?

    Quote Originally Posted by chem geek
    Wow, 30 ppm FC with 30 ppm CYA is actually a lot higher, but of course there's a lot of possible error in the CYA measurement. It's roughly equivalent to 5.4 ppm FC with no CYA so that's high.
    Well i read the postings here from some research about drinking chlorinated water where they found no ill effect other than taste up to what was it, 20-30 ppm cl. They said no inflammation of mucous membranes under that point, thats why I figured it would be fine. If you can drink 20ppm without irritation short term, then swimming in it should be fine as well short term. We are aiming now at 10ppm with 40cya, (i usually forget to test, and it is around 5fc that i add more)but I think its definately the cc that are bad. Last year we just had pucks floating and the water was semi clear with fc around 3 (from strips, no cya measure) and you could smell the cl smell, and it was a little irritating to the skin when you could smell it. We tried using less cl because of it, and just lived with a cloudy pool and manually removing the backswimmers.

    It took a while form the cl to drop under 10fc, but my wife commented on how nice the water felt.
    She was also surprised that there was no smell, because the pool often had one last year.

    The vinyl hasn't bleached one bit either

    Oh yea, the way it got so high, I forgot to set the bleach to 12.5% on the calculator and added the wrong amount.

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