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Thread: Confused about FC

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    Confused about FC

    Hi guys,
    We have a new above-ground 10'x30" steel-frame pool.

    We filled it up and the kids played for a few days and then I found this website and realised that I needed to put chemicals in the pool. The water had got a bit cloudy (I think my youngest may not have been getting out to pee...) We drained the pool, scrubbed it and re-filled it.

    The kids played in it for a day or so when we first re-filled it before I had a chance to get to the store for bleach and a test kit, but it was not cloudy at all this time (we gave the kids a big lecture!)

    So, I bought a simple test kit (NOT strips!) and put the appropriate amount of chlorine in (as determined through the pool math calculator).

    When I went to check the levels an hour later, the chlorine was not registering.

    I added the same amount of chlorine again and tested 30 minutes later and then again a few hours later and still at zero for chlorine.

    I then read that it may be that the pool needed to be shocked, so I did the math on that and added the appropriate amount of bleach, as well as some CYA in a sock in the skimmer basket (the temp. has been in the high 30s recently so I was worried that the heat from the sun was burning up the FC quickly). I let the pump run all day and tested the levels and the chlorine was off the chart as was the PH. That was three days ago.

    Two days ago I tested the levels again and both Ph and FC had come down but were still at the top of the scale and too high, so I left it for another two days.

    Today I checked the levels and FC is not registering at all, but the Ph is perfect.

    How can I get the FC to the correct level without altering the Ph? and can my kid swim in it like this (he's desperate, having had to wait three days already)?

    I'm really confused by all the chemistry... any help greatly appreciated!
    Thanks!
    Joy

    FC - zero
    Ph - 7.6
    Capacity of pool: 1236 gallons
    10'x30"
    10'x30"
    above ground
    metal-frame
    temporary pool

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    pabeader's Avatar
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    Re: Confused about FC

    What strength and age bleach?
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Mod Squad JohnT's Avatar
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    Re: Confused about FC

    Welcome to TFP!

    You really can't go two days without testing chlorine levels. Without knowing your CYA level and what levels you are seeing with FC, we really can't offer much advice.

    Though high chlorine levels can interfere with pH readings, chlorine and pH are not at all related and are managed separately.
    TFP Moderator
    20K Gallon 20X36 Vinyl Inground
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  4. Back To Top    #4

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    Re: Confused about FC

    Quote Originally Posted by pabeader View Post
    What strength and age bleach?
    It is brand new bleach, 10.3%
    10'x30"
    above ground
    metal-frame
    temporary pool

  5. Back To Top    #5

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    Re: Confused about FC

    We weren't going in the pool during that time so I didn't think it mattered - wasn't able to test as we were away at a wedding.
    10'x30"
    above ground
    metal-frame
    temporary pool

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    Re: Confused about FC

    What test kit did you get?
    Yellow & red drops?
    16' x 34' vinyl in ground - 16,500 gal.
    Hayward EC-75 DE filter with Hayward 1hp Super Pump
    TF-100XL Test Kit with SpeedStir

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    Re: Confused about FC

    Quote Originally Posted by Mike1162 View Post
    What test kit did you get?
    Yellow & red drops?
    Yes - it was the only one I could find in town (other than test strips, which I read on here were bad)
    10'x30"
    above ground
    metal-frame
    temporary pool

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    Re: Confused about FC

    That's a very common test kit. It actually doesn't test FC (Free Chlorine). It tests TC (Total Chorine). The 3rd type of chlorine we are concerned about is CC (Combined Chlorine).

    Free Chlorine is the chlorine that is still good. By good I mean available to kill (oxidize/sanitize) the bad stuff in the water.
    Combined Chlorine is basically used up chlorine.
    Total Chlorine = Free Chlorine + Combined Chlorine. It's kind of useless to test for Total Chlorine if you are having problems like cloudy water & don't also know what the Free Chlorine and/or Combined Chlorine levels are.
    16' x 34' vinyl in ground - 16,500 gal.
    Hayward EC-75 DE filter with Hayward 1hp Super Pump
    TF-100XL Test Kit with SpeedStir

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    Re: Confused about FC

    The test kit said that if you test the water within 10 seconds, that gives the FC reading and then waiting 5 mins gives you the Combined Chlorine reading... so I was going off that.

    Bottom line, can my kid swim in it as it is or is it dangerous?

    We don't have a ton of money, the pool itself was a gift from my parents for their grandkids and I have already spent more than the cost of the pool on chemicals/cover/vacuum/test kit etc. The FAS/DPD chlorine tests that I have seen online are the price of our whole pool. is there no way for me to do this method without buying one?
    10'x30"
    above ground
    metal-frame
    temporary pool

  10. Back To Top    #10
    Mod Squad JVTrain's Avatar
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    Re: Confused about FC

    Pool School - Guide for Seasonal/Temporary Pools

    I'd follow that guide for a pool that small. If need be, drain and start over if the water looks suspect right now.

    Your pH is going to rise because likely the TA in your water is higher than optimal. If your TC is zero, you need more bleach! You also need some source of acid to bring the pH down when it rises. Muriatic acid is cheapest but for a small pool, powder pH reducer is simpler.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
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    Mod Squad pooldv's Avatar
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    Re: Confused about FC

    Chlorine level is set based on CYA and the Chlorine CYA Chart. Always keep FC at or a little above target and never let it drop below minimum or the pool will be unsanitary and algae will grow.

    It is safe to swim when
    PH is 7.2-7.8
    FC is above minimum
    FC is below shock level
    Water is clear
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    Re: Confused about FC

    AWESOME!! Thank you so much!
    There is tons of information on this site but I have having trouble navigating it all. This is very helpful! Thank you thank you!
    10'x30"
    above ground
    metal-frame
    temporary pool

  13. Back To Top    #13

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    Re: Confused about FC

    Ah - you didn't mention that you'd get a chlorine reading after a few minutes. That is an indication that you have no FC & the TC is all CC.

    Bottom line is I wouldn't let anyone in the pool without FC.

    Your best bet may be to drain & refill the pool again. Then immediately add enough bleach to bring the Chlorine level up to 3 or 4 ppm. You then need test every day & make sure the level doesn't fall below 2ppm during the afternoon. After a couple days you'll know how much to add in the evening to maintain the minimum through the afternoon when the sun is burning off chlorine. Oh yeah, don't forget the CYA.
    16' x 34' vinyl in ground - 16,500 gal.
    Hayward EC-75 DE filter with Hayward 1hp Super Pump
    TF-100XL Test Kit with SpeedStir

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