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Thread: CH low after drain/fill

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    CH low after drain/fill

    Hi,

    I'm new here and had a question about my CH level. I drained/filled my pool after new tile and have the following numbers:

    25k gal, inground, gunite, chlorine,

    FAC 0
    PH 7.8
    TA 80
    CH 80
    CYA 30
    Phosphates 100

    After filling I shocked it and all chlorine was gone within a day. My plan is to first raise CH.

    I purchased dowflake. The pool calculator has me adding about 35lbs of Dowflake. Is there a limit I should add at a time? Also, any idea why my FAC is dropping to 0?

    Thanks for any info.

    John

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    Re: CH low after drain/fill

    Welcome to TFP!

    I would start with about 80 ppm of calcium. After that, it will be easier to get the rest of the calcium in without any clouding if you lower the PH to around 7.4 or 7.5. Remember that you don't want to do anything that will raise the PH for hours after adding calcium, particularly as you are approaching the proper levels (this is not much of a problem for the first addition).

    The most common cause rapidly falling FC levels is algae. You might be right on the edge of an algae bloom. It would be best if you brought FC up as soon as possible, otherwise the algae might get ahead of you and be much tougher to kill.

    If you get a lot of direct sunlight it is also possible that you aren't used to how rapidly FC levels go down when CYA is only 30. I would expect you to lose 40% to 80% of your FC each sunny day, depending on how much sunlight the pool gets and how warm/cold the water is.
    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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    gtm's Avatar
    Join Date
    Aug 2008
    Location
    St. Petersburg, Florida
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    Re: CH low after drain/fill

    This is probably off the wall, but John said that he's just finished refilling. In my city they say that the water leaving the plant is 4-6 ppm chloramines, and I measure 2-3 ppm CC out of the hose. If John's town is similar, might the FC be dropping quickly at first in order to break down the CC that came in with the fill water?

    Just FWIW, Gary
    15,000 gal. IG fiberglass pool w/ 1 hp Hayward Max-Flo and 250 lb. Hayward sand filter
    Located in St. Petersburg, Florida, and enclosed in a birdcage

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    Guest

    Re: CH low after drain/fill

    Not off the wall at all. Very possibly what is occurring. Testing for CC would tell! When the fill water has chloramnes it's a good idea to shock after a refill to get rid of them.

  5. Back To Top    #5

    Re: CH low after drain/fill

    Thanks for all the info. I added the 80ppm of calcium. I premixed before adding it in. The water is cloudy. I assume that is because of all the calcium. Is that correct? Should I continue raising calcium despite no FC or should I shock now and add more calcium after shocking?

    After addding calcium and shocking these are my numbers:

    FAC 4
    PH 7.6
    TA 90
    CH 190
    CYA 24

    Should I add calcium or is 190 good?


    John

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    JasonLion's Avatar
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    May 2007
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    Silver Spring, MD
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    Re: CH low after drain/fill

    You don't want to shock and be adding calcium on the same day. With CH at 190, raising the CH level further is still worth it, but is no longer the top priority. Get the water cleaned up and the FC holding steady before raising CH further.

    The water might well be cloudy from calcium, it could also be algae. Calcium clouds tend to be white to light gray. Algae tends to make the water green or dark gray or brown. For calcium clouding you should lower the PH just a little, say to 7.4 or 7.5 and it should clear up in a day. If it is algae the FC level will fall rapidly and you need to shock the pool.
    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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