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Thread: Fiberglass pools and CYA

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    Fiberglass pools and CYA

    I wish I had found this forum before I Opened the pool this summer!
    I have a fiberglass pool and therefore it is not to be drained unless the water is pumped out from underneath (huge hassle), and my cya level is high at 80.
    I live in Toronto so the pool is only used 3 months per year and this is my second year. The pool has a copper ionization system and a puck feeder. Due to a bylaw here a saltwater pool would have cost a crazy amount given the sewer access at my house (don't ask the bylaw is too strange to explain).
    My question is how much can I lower the CYA levels by exchanging a several inches of water each week? Is liquid chlorine safe for fiberglass pools?
    Pool is clear, I just shocked the pool to re-establish chlorine after these test results
    Lab results: tc .6 and fc .3
    CYA 80
    TA 110
    Ca 125
    pH 7.3

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    Join Date
    Feb 2008
    Flower Mound, TX

    Re: Fiberglass pools and CYA

    Welcome to TFP!

    If you stop using tablets and go to bleach, you can live with a high CYA like that. By chlorinating using the cholrine/CYA chart at pool-school/chlorine_cya_chart_shock, you will know just how much FC you need to operate on a day to day basis.

    You can lower your CYA by replacing water a few inches at a time. It just takes a long time.

    With a CYA of 80, your absolute minimum FC should be 6 ppm. You are going to have an algae outbreak soon if you don't raise your FC. You also need to consider getting a test kit that has the FAS/DPD chlorine test as this allows you to test for FC levels above 5 ppm, essential for shocking. Please consider not using your copper ion system as well. Copper is what stains hair and pool surfaces green. There is no need for an ion system when your pool is properly chlorinated.
    10K gallon IG gunite with waterfall; Pentair CC320P filter; WhisperFlo 2 HP pump
    TF Test Kits - Pool Math - Pool School
    "It depends."- JohnT

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    In the Industry
    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: Fiberglass pools and CYA

    My question is how much can I lower the CYA levels by exchanging a several inches of water each week?
    AS much as you want. If you drain/refill10% of your water you will have 10% less CYA, etc.

    You can do it simultaneously quite easily. Pump off. Assuming your fill water is colder than the pool, start refilling by sticking the hose in the bottom of the deepest point. Then start siphoning from the opposite end of the pool and only go maybe a foot below the surface. You could lover your CYA down to a manageable 40 or so in very short order and never change the level of the pool water.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Fiberglass pools and CYA

    Thank you for your responses, the problem seems to be getting a lot better (I think). After having lots of canon balls and replacing some water the latest tests are as follows:
    Tc: 1.6
    Fc: 1.3
    pH: 7.5
    CYA: 70
    Ta: 100
    Now I just have to learn to use liquid chlorine (a slightly daunting task). Wish me luck
    Fiberglass pool 11x24 in Toronto

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    elwood58's Avatar
    Join Date
    May 2012
    Sun City West Arizona (2nd Home)

    Re: Fiberglass pools and CYA

    Good job so far, but you need to get that chlorine up. At least in the 3-5 ppm range. Without a margin of free chlorine, you run the risk of a storm, or even a really sunny day, putting you at a chlorine deficit, and then you get to go though the shock process. Use the pool calculator, and get some 6% bleach.
    14100 Gal IG MiniPebble, Pentair Intellichlor IC-40 SWG, Sand Filter, Pop Up Cleaning, Intelliflo VS Pump, Aquacal Heatpump/Chiller, 1/4 Acre Desert Landscaped, Lots of Deck. Built in 1984, updated in 2012 and 2014
    "If you don't measure it, you can't manage it!"

  6. Back To Top    #6

    Re: Fiberglass pools and CYA

    With a CYA level of 70 or 80, it shouldn't take a long time to lower to 40-50. If it were me, I would just go cold turkey on the stabilized chlorine and let the level fall slowly on it's own as water evaporates, splashes out etc and is replaced.
    10,000 gallon
    Viking Freeform Fiberglass Inground Pool. FNS Plus DE Filter Pentair Challenger .75hp pump


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