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Thread: Mysterious Increase in FC

  1. Back To Top    #1


    Join Date
    Apr 2008
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    Suffolk, VA, US
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    Mysterious Increase in FC

    My chlorine has increased from 6.0 to 26.0 in a matter of two days.

    In that time-frame, the only changes that occurred were: 1. installation of a solar cover, and 2. Autopilot changed it's percentage from 30% to 87% due to temperature increase. I have not added any external sources of chlorine.

    In my searching the forum for this issue, the only other case turned out to be the OP testing the water with the wrong reagents. I can assure you that is not the case here. I'm a long-time user of the TF-100 test kit, I have brand new reagents that I received 10 days ago and I've even repeated the test multiple times since last night's discovery. Even this morning, I read 26.0. (So no overnight loss, yay!)

    Prior to installing the solar cover, my readings from last week included 5.5, 2.5, 8.0, 7.0 and 6.0 as I was dialing in my SWG percentage after SLAM was finished. CC has been zero with all post-SLAM tests. Everything was fine at 6.0 for several days prior to installing the solar cover.

    I can only assume that the solar cover has eliminated FC loss due to sunlight, and this caused a build up of FC even more-so because the SWG raised it's percentage quite a bit.

    So the question is: what to do about it? For now, I'll be removing the cover during the day. I have also reduced the SWG to 0% until I get back to a normal range.

    I'm concerned about this upcoming weekend which is our first pool party. What is the highest FC that is still considered safe for swimming? If things aren't in check within a day or so, would it be crazy to intentionally introduce some leaves or grass clippings in a net to try and "use up" some of the FC?

    Btw, the solar cover is a Blue Wave 20-Feet x 40-Feet Rectangular 12-mil Solar Blanket, purchased from Amazon.

    Thanks for any and all feedback,

    Kelly
    Rectangular Vinyl 20' x 40', 3.5' shallow end, 8' deep end, approx 33,000gal
    1.5 HP Pentair WhisperFlo / 60 gal DE Filter / 2 returns - 1 shallow end wall, 1 deep end floor
    SC-60 SWG / Autopilot Digital Pool Pilot v.4.2 / Polaris 280 w/ Booster Pump
    TF-100 Test Kit

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    Join Date
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    Re: Mysterious Increase in FC

    By turning up your SWG, then covering the pool, you have done two things:
    1. Increased FC production
    2. Protected from FC loss

    So, yes, your FC will go up.

    Turn off the SWG, uncover the pool, and FC will go down naturally.

    You can swim up to shock level as calculated by Pool Math. It'll go down pretty quickly though, I bet.
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
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    Re: Mysterious Increase in FC

    Ok thanks Robbie. Lesson learned: If I choose to cover during the day, turn SWG off.

    Looks like my shock level is 31.0, so by your safety criteria I should be fine. Looking forward to tonight's test result - did I understand right that rate of FC loss is proportional to FC? So a higher FC dissipates faster than a lower FC would?
    Rectangular Vinyl 20' x 40', 3.5' shallow end, 8' deep end, approx 33,000gal
    1.5 HP Pentair WhisperFlo / 60 gal DE Filter / 2 returns - 1 shallow end wall, 1 deep end floor
    SC-60 SWG / Autopilot Digital Pool Pilot v.4.2 / Polaris 280 w/ Booster Pump
    TF-100 Test Kit

  4. Back To Top    #4

    Join Date
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    Dallas, TX
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    Re: Mysterious Increase in FC

    Yes, it will. I can't give you the math or the ratio, but it's true. High FC in relation to lower CYA will burn off pretty quickly.
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
    If TFP has helped you, please click to SUPPORT TFP!

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    Join Date
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    Re: Mysterious Increase in FC

    Chiming in with an update:

    Last night's test showed FC at 19.5, so a loss of 6.5 during the day yesterday. Cover is off again today, so looks like I'm well on my way to enjoying the pool this weekend.

    We've made it standard daily procedure to remove cover in the morning, replace it in the evening.

    Now... the real trick is going to be: Remembering to turn the SWG back on when FC drops to acceptable level!
    Rectangular Vinyl 20' x 40', 3.5' shallow end, 8' deep end, approx 33,000gal
    1.5 HP Pentair WhisperFlo / 60 gal DE Filter / 2 returns - 1 shallow end wall, 1 deep end floor
    SC-60 SWG / Autopilot Digital Pool Pilot v.4.2 / Polaris 280 w/ Booster Pump
    TF-100 Test Kit

  6. Back To Top    #6
    Mod Squad pooldv's Avatar
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    Re: Mysterious Increase in FC

    Good plan!
    TFP Moderator
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    2012 build and pics, 20k gal gunite, black onyx pebblesheen, OK flagstone, IntellifoVS, cart filter w/Pleatco, IC40 SWG, Solartouch, 5 12'x4' solar panels, HP50HA heat pump, 8mil solar cover, borates, TF-100 test kit, SONOS, Doheny's Discovery Robot, hot tub on bleach

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