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Thread: Does cold water temperature affect chlorine test?

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    Does cold water temperature affect chlorine test?

    My pool is clean and up and running at a temp of 50. Just opened it last week. There is plenty of salt in it - my test said 3200 ppm (although the chlorinator's low salt light is on). When I add the DPD powder to test for FC the water stays totally clear. Last week (water was 56degrees) I had FC of 4. Is it possible that my test this week is not reliable due to the cold temperature? Could the powder have gone bad in the past week? Or is it accurate that I have no chlorine? The CYA level is also coming up as 0 (unmeasurable below 30). I've been maintaining my pool for 2 full years and this is a first for me. Thanks in advance!!!

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    Mod Squad YippeeSkippy's Avatar
    Join Date
    Jan 2012
    'burbs of Augusta, Georgia

    Re: Does cold water temperature affect chlorine test?

    Most SWG do not produce when water is that cold. I would think you very well may have no chlorine in the water and could use some liquid chlorine to spike it up until the water warms more. I'm sure that's also why you're seeing the low salt light.
    Maddie :) 12K Fiberglass IG, Infinity 4000 automatic cover, SWCG, Hayward Sand Filter, Hayward 1.5 Pump, Doheny Discovery Robot, Savi Melody LED pool lights, outdoor speakers and other assorted doo-dads. Sundance Altamar Hot Tub.
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    Richard320's Avatar
    Join Date
    Jan 2010
    San Dimas, CA (LA County)

    Re: Does cold water temperature affect chlorine test?

    Short answer: no.

    Long answer: many SWGs shut off at low water temperature, so you may not be producing any FC. If none is being produced, whatever you had will be long gone in a couple days. Cold water will slow the reaction in the CYA test, which can make you read falsely low. Scoop up a water sample and bring it inside and let it warm up to room temperature at least. Maybe set it in a sunny windowsill. Let the sample warm up before you mix it and then carry it outside into full sun and recheck that CYA reading.
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    daleyfolk's Avatar
    Join Date
    Jul 2014

    Re: Does cold water temperature affect chlorine test?

    My water is 55F and I'm getting sensible FC readings. (With last year's test kit)
    17.5 K gallons (16x32) vinyl inground pool with 1 hp pump and an old Triton sand filter. >20 years old. New 2015 Rheem gas heater. TF-100 Test kit. Little red robot and a Pool Blaster Max.

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