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Thread: Large Drop in CYA over Winter

  1. Back To Top    #1

    Join Date
    Feb 2011
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    Large Drop in CYA over Winter

    I just popped a couple of straps loose to get a water sample since I will be pulling cover off tomorrow (mesh cover). I tested my water and got the following: FC = 0 of course; CYA - I filled all way up and still saw dot so I have to estimate between 5-10; TA = 60; PH = 7.5

    Weird thing is that I'm pretty sure when we closed pool CYA was around 30ish. Water temp of sample is about 70 F.

    Also, at the end of last year I believe I was fighting MA. Therefore, I stocked up on the Menards bleach sale today only to come home and find out I have such a low CYA I can't read it. I guess I will have plenty of bleach since it won't take me nearly as much as I was thinking.

    My question is is it normal to lose CYA over the winter in a seasonal pool?

    Also, my understanding to kill MA is to follow normal shock process until passing the overnight test and then bring to MA level. How long do I maintain MA level? One more question. If I don't actual see any MA when I pull the cover and look around does it mean I don't have any or can it just go dormant and wait to grow?

    Thanks
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  2. Back To Top    #2

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    Re: Large Drop in CYA over Winter

    CYA can be lost over the winter due to a process that has been known to occur when the FC drops to zero. See this link for a detailed explanation but basically, it isn't as uncommon as we once thought.

    degradation-of-cyanuric-acid-cya-t8880.html

  3. Back To Top    #3
    frustratedpoolmom's Avatar
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    May 2007
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    SWSuburban Chicago, IL
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    Re: Large Drop in CYA over Winter

    Quote Originally Posted by briansturgeon
    Also, my understanding to kill MA is to follow normal shock process until passing the overnight test and then bring to MA level. How long do I maintain MA level? One more question. If I don't actual see any MA when I pull the cover and look around does it mean I don't have any or can it just go dormant and wait to grow?
    We like the water to circulate for several hours before we test... your numbers may change - just an FYI.

    IF you proceed with MA level shock, 24-48 hours should suffice. If you don't see what you suspect was MA, I would wait until you do before you bother.
    Helpful links: Pool School; CYA/Chlorine Chart
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  4. Back To Top    #4

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    Mar 2012
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    Re: Large Drop in CYA over Winter

    I was between 30-35 CYA last year when closing and also opened this year to unreadable CYA levels. I have since added almost 2 Kg of CYA since opening last weekend and I am just now reaching 30ppm. Then again here in Ontario I drain below the returns and refill with clean unstabilized water every spring. So no surprise for me.
    21K gal, Vinyl, 16X32, 3/4 HP Hayward Maxflo, Hayward Pro 24" Sand Filter
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