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Thread: What happens to CSI in the winter? Should I worry?

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    svenpup's Avatar
    Join Date
    Nov 2009
    Sacramento, CA

    What happens to CSI in the winter? Should I worry?

    Thanks to you guys I got my CYA down to a reasonable level and my pool is balanced. I have boric acid on the way, and I am thinking about doing 2000 ppm of salt (basically I do whatever Waterbear says) .

    I have been playing with the calculator, and I have a hypothetical question...

    If I plug in normal target levels:

    • pH 7.7 (I read that once the borates are in, the pH will tend to buffer to ~7.7)
      TA 75
      CH 300
      CYA 40
      Salt 2000
      Borates 50

    With a temp of 70 I get a CSI of -0.22 which is on the low side of balanced.

    My question is, what happens when winter comes and the pool temp drops? The values of TA, CH, CYA, Salt, and Borates are going to stay fairly constant without intervention.

    Even at 60 degrees, the CSI is in the "Potential to become corrosive" range and obviously gets worse as you approach freezing.

    Am I missing something? Will the pH tend to rise automatically as the temperature drops??

    Should I jack up the pH as the temp drops?

    inquiring minds want to know
    TFP Method Advanced Intermediate
    • 17,500 gallons - In Ground - Plaster - Hayward Swimclear 3020 Cartridge Filter - Sta-Rite Max-E-Glas Main Pump upgraded with A.O. Smith B2980 E-Plus New Centurion Two-Speed Motor - Polaris 280 Cleaner with Polaris PB4-60 Booster Pump - TightWatt2 Timer - Taylor K-2006 Test Kit - Pool Pilot Digital Nano SWCG

    Helpful Links: Pool School, BBB for Beginners, How to Shock ('s a process not a product), Chlorine/CYA Chart, Jason's Pool Calculator

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: What happens to CSI in the winter? Should I worry?

    This is really a Deep End topic.

    Assuming the pool is covered for the winter, which keeps things fairly stable in most ways, the PH will go up as the temperature goes down, more or less canceling out the change in CSI from the change in temperature. So you don't normally need to worry about it. If the pool is left open, you should allow the natural rise in PH as the water gets colder, to keep CSI balanced.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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