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Thread: desired chlorine level when closing pool with solid cover

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    desired chlorine level when closing pool with solid cover

    I have about 6ppm right now (cya 50-60) and closing in 18hr with one of those $2,500-3k anchor solid covers. Is that OK?

    Also, guys who will close my pool may shock it. Last two closings they used non-chlorine shock oxidizer ("GLB 3 part system" and the following year "AquaZone winterizing Chemical kit"), I don't know what they'll use this time, but if it's based on chlorine - should I let them shock?

    Someone at pool store said high chlorine level will cause pool cover to deteriorate and advised to have no more than 2ppm. True/False? Doesn't sound right, closing instructions don't mention that, but just want to double check in regards to expensive solid cover


    Thanks
    Bill
    18'X4' 7600 Gal AG
    3/4 HP Pentair Pump
    Hayward S166T 100 lb sand filter

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    Mod Squad jblizzle's Avatar
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    Re: desired chlorine level when closing pool with solid cove

    Probably too late, but raising the FC up to shock level for your CYA would not be a problem and would be recommended I think to hopefully open to a clear pool in the spring ... assuming your water is around 60 degrees already.

    Sounds like the Pool Store does not understand the CYA/FC relationship ... 2ppm might be close to enough with 0 ppm CYA.
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    Re: desired chlorine level when closing pool with solid cove

    I just want to make sure 6ppm won't hurt solid cover. The pool is closed, but I may contact the cover manufacture, see what they say. thanks
    Bill
    18'X4' 7600 Gal AG
    3/4 HP Pentair Pump
    Hayward S166T 100 lb sand filter

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    Mod Squad jblizzle's Avatar
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    Re: desired chlorine level when closing pool with solid cove

    My guess is the cover manufacturer does not understand the FC/CYA relationship either. I can not think of why you would not be safe up to shock level which is around 20ppm.

    This chart shows the active chlorine level depending on CYA level:
    http://richardfalk.home.comcast.net/~ri ... l/HOCl.htm

    As you can see 20ppm FC at CYA of 50ppm has an active FC level of 0.30
    At 0ppm CYA (which seems like what the pool industry quotes) and 2ppm of FC the active level is 0.97

    So triple the active chlorine of the buffered water with a 20ppm FC.

    In other words, you would do ~3 times more damage with 0 CYA and 2ppm FC than at 20ppm FC at 50ppm CYA.
    Jason, TFP Moderator
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    Re: desired chlorine level when closing pool with solid cove

    Quote Originally Posted by jblizzle
    In other words, you would do ~3 times more damage with 0 CYA and 2ppm FC than at 20ppm FC at 50ppm CYA.
    This is true from a reaction rate perspective, but if the chlorine were to react with the cover and get used up doing so, then 2 ppm would have less cumulative damage than 20 ppm, but that assumes that more than 2 ppm would react with the cover even with the slow reaction rate when CYA was present.

    Bubble-type covers typically last only 2-3 years though some of their degradation comes from heat and UV, but the degradation of the bubbles is mostly from the chlorine. My mostly opaque electric safety cover lasts around 3-4 years so I'd expect a winter cover to last at least that long (in terms of degradation from chlorine) since it's only used during the winter, but it could get damaged in other ways from weight stress.
    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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    Mod Squad jblizzle's Avatar
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    Re: desired chlorine level when closing pool with solid cove

    Quote Originally Posted by chem geek
    Quote Originally Posted by jblizzle
    In other words, you would do ~3 times more damage with 0 CYA and 2ppm FC than at 20ppm FC at 50ppm CYA.
    This is true from a reaction rate perspective, but if the chlorine were to react with the cover and get used up doing so, then 2 ppm would have less cumulative damage than 20 ppm, but that assumes that more than 2 ppm would react with the cover even with the slow reaction rate when CYA was present.

    Bubble-type covers typically last only 2-3 years though some of their degradation comes from heat and UV, but the degradation of the bubbles is mostly from the chlorine. My mostly opaque electric safety cover lasts around 3-4 years so I'd expect a winter cover to last at least that long (in terms of degradation from chlorine) since it's only used during the winter, but it could get damaged in other ways from weight stress.
    I figured I had over simplifed it

    I see what you are saying, I guess what I stated would only be ~correct if you were actively maintaining the 2ppm and 20ppm of FC. If once the 2ppm is gone it is gone ... and I could see how the higher FC would still be "reacting".
    Jason, TFP Moderator
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