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Thread: Should you ever lose FC overnight?

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    Should you ever lose FC overnight?

    Hey guys,

    Opened my pool last Saturday. Got Ph and Alk in line and pretty clean by Sunday and SLAMED that night. The pool was cloudy. Later that night but after at least 3-4 hours after Slammimng, my numbers looked like this:

    Sunday Night

    FC - 24
    CC - 0
    PH - 7.2
    Alk-110
    CYA-60


    In the morning my FC had held, so I didnt do anything, FC has gone up a little I assume form the extra circulation.

    Monday Morning -

    FC - 27
    CC- 0
    PH - 7.2
    Alk-110
    CYA-60

    All day Monday it was sunny - I didnt do anything - pool had cleared up a lot

    Tuesday morning I checked and my FC had dropped from 27 to 18. (again this was in a 24 hour period). Pool cleared up perfectly, crystal clear. However, I felt that was a rather big drop, and toyed with the idea of bring the FC back to shock level, but decided to do a test later that night and compare numbers in the morning. So I tested last night (Tuesday)before bed and the FC level was at 14 and CC was 0 everything else held.. I checked first thing in the morning today and my FC was 11. ( so it dropped 3 more ppm over night) CC is .5. I should mention that when I SLAM the pool I only use 5mL of sample and multiply by 1 for equivalance so I dont go through so much reagent, I'm sure its not as accurate this way, but it kills me to go through 50 drops of 8071.

    So my question is should you have any FC loss at night as I did last night or is that a sign I did not SLAM correctly by only making sure it held on the first night? Or is it that once the FC level starts to drift down from a very high level it will do so even at night? If this is not normal, I assume I can bring levels back to shock value once again. Pool is crystal clear and freezin cold so no one is going in....

    Thanks!
    38,000 gallon vinyl liner, True "L", Sand Filter, Hayward Heater, Diving Board

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    cowboycasey's Avatar
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    Re: Should you ever lose FC overnight?

    The best way is to keep your FC at SLAM level until you pass all 3 parts of the OCLT, you have 1, clear water but the other 2, 0 CC and no drop in FC over night did not pass.. take it back to SLAM and keep it at 24fc (for your 60 CYA) as much as possible until all 3 tests have been passed

    With clear and cold water it should go pretty fast
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  3. Back To Top    #3

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    Re: Should you ever lose FC overnight?

    Thanks for the reply. The first night I Slammed it held, but your saying that doesnt count because the water wasnt clear yet? Therefore, FC should always hold overnight?
    38,000 gallon vinyl liner, True "L", Sand Filter, Hayward Heater, Diving Board

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    Mod Squad woodyp's Avatar
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    Re: Should you ever lose FC overnight?

    A one day SLAM didn't take care of your issues if you are losing 3ppm over night. 1 ppm or less is the goal. and you already know 5 CC ain't what we're lookin' for! Back to the SLAM for you! Stay with it.
    16x32x52" Steel Cornelius Miramar AGP Vinyl liner 13,100 gal. Buried 2 ft.
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    Texas Splash's Avatar
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    Re: Should you ever lose FC overnight?

    When I read your first post, I didn't really count that first OCLT as passing because of the inconsistency of the FC testing. Remember how the first FC appeared to be 24, but then when you tested the next day it was 27? So something wasn't right - circulation, # of drops, something. Now if your first test would've been 27 or 28, then that would've looked better. But I agree with Casey, something is happening in your water, and the sooner you hit it the sooner you'll be back to regular levels and no worries. The 1 ppm rule of overnight loss was established by the TFP staff after many years of analysis and computations which also resulted in the Chlorine/CYA Chart. As long as the FC level is at least 3 ppm up to someone's FC SLAM level for their current CYA, the 1 ppm rule is a reliable yardstick to know if there is a need to SLAM.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
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  6. Back To Top    #6

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    Re: Should you ever lose FC overnight?

    Just to be clear my CC is .5 not 5...

    Thanks guys.
    38,000 gallon vinyl liner, True "L", Sand Filter, Hayward Heater, Diving Board

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    Re: Should you ever lose FC overnight?

    Just to be clear my CC is .5 not 5...

    Also I just re-ran the FC and CC using 10 ml of water. FC = 14, and CC is pretty much zero....a very slight, slight pink tinge...maybe at lower levels using 5 mls is not that accurate?
    38,000 gallon vinyl liner, True "L", Sand Filter, Hayward Heater, Diving Board

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    Texas Splash's Avatar
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    Re: Should you ever lose FC overnight?

    10 ml is definitely better for accuracy. Might not hurt to run your FC elevated today and run one more good OCLT tonight using the 10 ml sample. See how it goes. Your situation may be short-lived.
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
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  9. Back To Top    #9

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    Re: Should you ever lose FC overnight?

    Thats what I'm thinking....bring it up to shock level during the day..take a reading tonight and again tommorow, doing the non-cheapo 10 ml method....thoughts? And thanks for the help...!
    38,000 gallon vinyl liner, True "L", Sand Filter, Hayward Heater, Diving Board

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    Texas Splash's Avatar
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    Re: Should you ever lose FC overnight?

    I agree. Good luck!
    Pat (a.k.a. Texas Splash) ~ My Pool: Viking Fiberglass; 17,888 Gal; Waterway Supreme 2-sp/2-hp pump; Hayward Ctg filter; TF-100 w/ Speed Stir
    Vital Links: POOL SCHOOL, RECOMMENDED LEVELS, RECOMMENDED CHEMICALS, Poolmath Calculator, SLAM, Chlorine/CYA CHART.
    If you enjoyed your TFP experience, please consider donating to Support TFP!

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