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Thread: FC Levels low daily

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    FC Levels low daily

    I'm not sure if I need to add CYA or what, but my FC levels are low every night. I test every evening after we're finished swimming and then add bleach. My levels get down to 1.5-2.5 generally. It's been a bit cloudy and we've had a lot of kids in the pool, so someone suggested getting it up to 10 the day before and the day after big parties. That had helped with the cloudiness, but the FC still gets low. Am I understanding correctly that it should not get below 4?

    Last night's #s:

    FC 1.5
    TA 90
    CYA 45
    Ph 7.5

    I tested a couple hours after I put in the bleach and the FC was 10.5. This morning it was 9.5. Tonight, after only me swimming, it was 2.5

    It has been Hot here in Seattle (90+), which is unusual for us. Is it possible I should raise the CYA? Should I just try to get the FC levels up higher in the evening?

    Is the end of the day the best time to test, or should I test earlier?

    Thanks all for your help!
    Sharon
    Seattle, WA; 9x18 Intex Ultra Frame, 4,800 gal; AG; Krystal Clear Model 635T Filter Pump; Bought 2013; TF-100 Test Kit

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    Swampwoman's Avatar
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    Re: FC Levels low daily

    If I understand you correctly, you lost 7 ppm of 10 ppm between doses, in less than 24 hours?

    You may be battling a nascent algae uprising with that kind of chlorine demand, which may have been caused by letting it drop below 4 ppm. Either that, or you have an unusually high usage rate due to organics or something else, like a pesticide spray, getting into the pool fighting the chlorine (unlikely, since your above ground.)

    In either case, I think you should do a careful overnight chlorine loss test first to confirm how much you lose overnight with no sunlight (see details in How to Slam in my signature). I believe a SLAM -- which, if your water is clear, will likely be a fairly short one -- will get you ahead and thus reduce your daily chlorine use.

    Even if you loose less than 1 ppm overnight, riding the chlorine higher for a few days may help. Also leave the filter running with the higher FC.

    Your CYA should be fine at that level...I'd start with increased chlorine and not letting it drop first, then if the consumption rate continues, explore the cya avenue further.

    Re: best time to dose...the benefit of night dosing as you're doing is more chlorine stays in at night with no sun to burn it off...so you're pretty much doing the optimal time. I dose in a.m. Just because that's when it's consistently convenient for me
    In ground extended Grecian, 22,000 gal, Hayward 220t sand filter, vinyl liner, dolphin m4 supreme.
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    Defgufman's Avatar
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    Re: FC Levels low daily

    Cloudiness sounds like algae....raise it to slam level after dark and do an overnight chlorine loss test first thing in the morning.
    Inground 13,200 gal Vinyl, Pentair 3/4 hp pump, Pentair Sand Dollar filter, Polaris 280

    Pool School, Pool Math, CYA to FC ratio chart, Testing Kits

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    Re: FC Levels low daily

    Thanks so much! I'll do that tonight. I've had trouble with algae in the past, but it was usually at the end of the season or when it was cloudy and cool. I have had some trouble with cloudiness, but I have been upping the FC at night to 10 when I know we'll have a lot of swimmers. Hopefully the SLAM will help!
    Sharon
    Seattle, WA; 9x18 Intex Ultra Frame, 4,800 gal; AG; Krystal Clear Model 635T Filter Pump; Bought 2013; TF-100 Test Kit

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    Divin Dave's Avatar
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    Re: FC Levels low daily

    If you do an Overnight Chlorine Loss Test, you can confirm if you have organics (algae) consuming your chlorine.
    Pool School - Perform the Overnight FC Loss Test (OCLT)

    If you have 1 or more ppm FC loss, you need to slam to full completion.
    Divin Dave,
    IG Vinyl, 15' x 30', 3 1/2' - 6' deep, Oval, ~15K gal, Intelliclor IC40, Intelliflo VS pump, Clean and Clear 420 Filter, auto-fill-disabled, Retrofit LED Color Light, Dolphin Nautilus Robot, TF100 Test Kit, Taylor K1766 Salt Test Kit, Tftestkit Pressure Gauge.
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    Re: FC Levels low daily

    So, I'm confused about raising the FC. I had a FC of 4.0 today after no one had been in the pool. I used the calculator to raise it to 16, per the chart. It said to at 86 oz of bleach. I tested two hours later and the FC is 27.5! Is it supposed to go that high?
    Sharon
    Seattle, WA; 9x18 Intex Ultra Frame, 4,800 gal; AG; Krystal Clear Model 635T Filter Pump; Bought 2013; TF-100 Test Kit

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    domct203's Avatar
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    Re: FC Levels low daily

    If your testing is accurate I would say that either your chlorine is stronger than the % you used in poolmath or your water capacity is incorrect. 4800 gallons in a 9x18 pool would require a water depth (not wall height) of 48".

    Reducing all those dimensions by 6" (8.5' X 17.5' X 3.5') brings capacity to 3900 gallons.

    Dom
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    Re: FC Levels low daily

    Dom, you're absolutely right about the pool capacity. It hadn't occurred to me to change that! I did check the % on the bleach, which is correct.
    The FC this morning is at 16.5 - quite an overnight loss. I'll keep testing to keep the FC up to 16 (using the correct capacity!!) throughout the day.
    Sharon
    Seattle, WA; 9x18 Intex Ultra Frame, 4,800 gal; AG; Krystal Clear Model 635T Filter Pump; Bought 2013; TF-100 Test Kit

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    domct203's Avatar
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    Re: FC Levels low daily

    Glad I could help.

    I've noticed that I overshoot a bit as well using my 6700 gal capacity, but I don't mind it for FC.

    Dom
    Dom - TFP Guide
    Intex 18' X 48" Ultra Frame AGP 6700 gallons | Two Intex CS8110 SWG's | Hayward Pro Series 21" Sandfilter | Hayward 1.5HP Power Flo Matrix pump | Hayward Thru-wall Skimmer | Wanda the Whale | 72 sq ft of Sungrabber Solar Panels with Hayward GLC-2P-A | Taylor K2006 Test Kit, Sample Sizer & Speed Stir | Click Here To Become a TFP Supporter!

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