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Thread: low FC again - rain or something else?

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    Join Date
    Mar 2013
    Location
    NW GA
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    low FC again - rain or something else?

    All this testing and balancing makes me

    Questions:
    Dropping chlorine - effect from heavy rains or indicative of need to shock?
    High TA - acid and aerate?

    Test Results:
    June 12 after 2+ inches of rain
    FC - 1
    pH - 7.1
    TA - 70
    CYA - 70
    Added bleach. FC up to 5 (tested 5 hours after bleach from arm's length depth at the side of the pool opposite where bleach was added)
    Dumb me forgot washing soda adds TA and I brought the pH up to 7.5 (and TA up over 100)

    June 13-16
    out of town, no tests, no swimmers other than the plethora of beetles that fall from the pine trees

    June 17
    heavy swim load of young kids, 1.5" of rain, no tests, SWG running at 50% for 12 hours

    June 18
    Backwash 2" from pool (roughly 800 gallons)
    FC - less than 1
    Added bleach. FC up to 5.
    It continues to rain another .5" or more of rain throughout the 18th after adding bleach.

    June 19
    FC is down to 1 again.
    pH - 7.5
    TA - 100
    CYA - I'm out of reagent

    I have CYA reagent on order.
    I have acid available if needed.
    Should we shock or wait and see if Chlorine level holds after the rain lets up?
    26900 gal IG Vinyl (18'x36', 3' shallow end and 8' deep end plus steps)
    sand filter and 2.7hp variable speed timer
    Jandy Ei SWG (2yr old)

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    Mod Squad Bama Rambler's Avatar
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    Re: low FC again - rain or something else?

    As a normal rule, rain makes very little difference in the pool balance. It may raise the pH a little but that's about all. I think you have something else going on.

    I would raise it to shock level and turn off the swg and run an OCLT.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

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    Smykowski's Avatar
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    Re: low FC again - rain or something else?

    You let your FC get too low, too often. Per the pool school chart, you should never let FC go below 3.

    Shock it.
    33' round, 23,000 gal AG vinyl , 1HP 2spd PowerFlo Matrix downsized with 3/4HP impeller (X2), Hayward S180T 150# sand filter (X2), Hayward H250 NG heater Pool Store year 1 - $850 for 2 months; Pool Store year 2 - $440 for 2 months, TFPC year 1 - $170 for 4 months; TFPC year 2 - $95 for 4.5 months
    The most important article on this site - The ABCs of Pool Water Chemistry

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    Join Date
    Mar 2013
    Location
    NW GA
    Posts
    69

    Re: low FC again - rain or something else?

    Thanks, both.

    FC maintained at 5 previous to now. All tests were within appropriate range since the pool was balanced back in March after opening routine.
    June 12 was the first low test so whatever is going on is new, and seems to be causing the low FC rather than due to "allowing" low FC. The water is clear and beautiful so hopefully oclt is 0 after shocking.
    26900 gal IG Vinyl (18'x36', 3' shallow end and 8' deep end plus steps)
    sand filter and 2.7hp variable speed timer
    Jandy Ei SWG (2yr old)

  5. Back To Top    #5

    Re: low FC again - rain or something else?

    We had a lot of rain a few days ago and ended up with a lot more dead bugs on our pool, and my FC did take a bit of a hit as a result (dropped to 4, I normally keep it at 6-7), but it didn't drop below what is safe for my pool, it was just lower than it had been. I added some bleach to make up the difference and it's been fine since.

    When you let your FC drop to basically 0 (however it happened) and you had swimmers before testing or adding more chlorine, you are probably now in the early stages of an algae bloom... it's going to use up what FC is in your pool pretty quickly, and not hold a stable level like it had been. It's kind of a chicken vs egg problem, but however it happened doesn't matter, the solution is still the same.

    If it were my pool, I'd shock just because the chlorine went low the first time - I wouldn't mess around and wait for it to get worse.
    Summer Escapes 15'x42" AGP, Intex 14" sand filter, Intex SWG

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