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Thread: CYA and FC?

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    CYA and FC?

    Hi all,

    I have a question regarding CYA level and FC. My pool is in direct sunlight for most of the day. I have opened the pool with success thanks to this site. My CYA is around 45. (I say around, because I'm not sure when you actually claim the black dot is no longer visible. It gets very faint at 45ish, but I can still barely see it if I squint very hard and focus on it from the beginning. If I have my wife look at it at 45 but not focus on it while filling the tube, she can not see it at 45.)

    Anyway, my FC will typically fall about 5 or 6 during a full day of sunlight. This is with good numbers on everything else using the TF 100 kit. MY CC is 0. Is this much of a fall in FC typical, or should I consider a higher CYA level? I'm nervous on raising my CYA level due to the cautions I've read hear about issues with a CYA level too high.
    12Kgal, AG, Sand, Hayward Swim Pro SW256T PAKS

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    Re: CYA and FC?

    Post up your full numbers for better help. If you are Going with 10 Fc lossing 5 fc per day would be about right for 45 cya. Might be good to raise it to 60 to see if that helps. I would do an overnight chlorine loss test before raising it just to be certain nothing is it your water which would be harder to kill with a higher CYA
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    Re: CYA and FC?

    Thanks. I have done the overnight test, and it indicates no FC loss. My pool is crystal clear, and I am not really having any issues right now. I just a new pool owner and want to make sure this FC drop in direct sunlight is the norm for the BBB method or if I need to raise my CYA level. I guess I'm also making sure I'm getting an accurate CYA result when testing since the CYA test seems to be a more subjective test. My numbers are (FC was before adding bleach to raise it):

    FC - 3
    CC - 0
    ph - 7.6
    TA - 110
    CH - 70
    CYA - 45
    12Kgal, AG, Sand, Hayward Swim Pro SW256T PAKS

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    Re: CYA and FC?

    5-6 ppm is a bit excessive for your CYA of 45. Average is normally about 2-3 ppm assuming very little swimmer load. YOu might have some invisible organics still in your pool.

    If you have not yet performed the OCLT, I would suggest doing that. Report the results
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: CYA and FC?

    Quote Originally Posted by duraleigh
    5-6 ppm is a bit excessive for your CYA of 45. Average is normally about 2-3 ppm assuming very little swimmer load. YOu might have some invisible organics still in your pool.

    If you have not yet performed the OCLT, I would suggest doing that. Report the results
    I have, and the FC holds with no drop. I suspect I may be reading the CYA level incorrectly in fear of getting it too high. Is there a guide regarding the test for CYA?
    12Kgal, AG, Sand, Hayward Swim Pro SW256T PAKS

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    Re: CYA and FC?

    Youtube video by TFtest kits
    http://www.youtube.com/watch?v=NxaqoW-_MCs
    24' 52" Above Ground
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    JasonLion's Avatar
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    Re: CYA and FC?

    Remember that the amount of chlorine you lose to sunlight depends on how high the FC level is to start with. Losing 5-6 out of 9-12 is normal. Losing 5-6 out of 7 means something is wrong.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: CYA and FC?

    Quote Originally Posted by JasonLion
    Remember that the amount of chlorine you lose to sunlight depends on how high the FC level is to start with. Losing 5-6 out of 9-12 is normal. Losing 5-6 out of 7 means something is wrong.

    Oh, ok. That makes more sense then, maybe. I've been adding enough to get it to 8 to 10 range anticipating the 5-6 drop throughout the day. I wasn't comfortable leaving it around 6 or 7 because of the drop I was seeing. Maybe I should try setting it to 6 or so to see if that helps.

    It doesn't make sense to me why the drop would be more when your FC is in the 9-12 range, but I will just accept that I guess. (The way my mind works, it's hard to accpet things with understanding the reasoning.)
    12Kgal, AG, Sand, Hayward Swim Pro SW256T PAKS

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    Mod Squad jblizzle's Avatar
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    Re: CYA and FC?

    Where are you located?

    I feel like I am experiencing the exact same thing as you. CYA of 45ppm and to keep the FC > 4ppm, I am having to add 5-6ppm everyday. Passed the OCLT multiple times.
    Jason, TFP Moderator
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  10. Back To Top    #10

    Re: CYA and FC?

    I'm from the middle TN area. What about you?
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    Mod Squad jblizzle's Avatar
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    Re: CYA and FC?

    I am in Tucson, AZ ... so the sun is a bit more extreme than you see. Add your location to your profile so it shows up.
    Jason, TFP Moderator
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    Re: CYA and FC?

    VOL,

    I believe the normal FC losses are on a percentage basis, so losing 5 ppm when you started with 10 is a 50% drop, but losing 5ppm if you started with 7 is about a 70% loss. So, if the 50% loss stays consistent and you start with 6, you *should* only lose 3 ppm or so, unless something else is in there trying to grow.
    Dedicated TFPer since 2012 with recommended test kit
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  13. Back To Top    #13

    Re: CYA and FC?

    I have been doing the same as well, starting at 12.0 every morning, down to 8.0 in evening but with swg producing 2 as well, so 6ppm loss altogether. CYA about 45-50. Even though I passed all 3 shock criteria several days ago, including a good oclt, this has been making me think something is "lurking". very reassuring that all is probably well.
    30000 gallon inground gunite pool
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    Re: CYA and FC?

    Quote Originally Posted by VOLmaniac
    Quote Originally Posted by JasonLion
    Remember that the amount of chlorine you lose to sunlight depends on how high the FC level is to start with. Losing 5-6 out of 9-12 is normal. Losing 5-6 out of 7 means something is wrong.

    Oh, ok. That makes more sense then, maybe. I've been adding enough to get it to 8 to 10 range anticipating the 5-6 drop throughout the day. I wasn't comfortable leaving it around 6 or 7 because of the drop I was seeing. Maybe I should try setting it to 6 or so to see if that helps.

    It doesn't make sense to me why the drop would be more when your FC is in the 9-12 range, but I will just accept that I guess. (The way my mind works, it's hard to accpet things with understanding the reasoning.)
    You lose a percentage rather than an absolute number.
    17,800 gallon, IG pool, 595 sq feet (17x35x4.5 avg rectangle), Hayward 525 cartridge filter, diamondbrite, 2 hp 2 speed hayward tristar filter, Stenner 45mhp10 automatically chlorinating

  15. Back To Top    #15

    Re: CYA and FC?

    Quote Originally Posted by Pauls234
    VOL,

    I believe the normal FC losses are on a percentage basis, so losing 5 ppm when you started with 10 is a 50% drop, but losing 5ppm if you started with 7 is about a 70% loss. So, if the 50% loss stays consistent and you start with 6, you *should* only lose 3 ppm or so, unless something else is in there trying to grow.
    Thanks, that makes sense then.
    12Kgal, AG, Sand, Hayward Swim Pro SW256T PAKS

  16. Back To Top    #16

    Re: CYA and FC?

    I am curious, because i don't own a pool myself, with adding bleach on a daily basis how much bleach do you go through in a week?

  17. Back To Top    #17

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    Re: CYA and FC?

    I am curious, because i don't own a pool myself, with adding bleach on a daily basis how much bleach do you go through in a week?
    Depends on the size of the pool, activity, CYA sunlight, etc.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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  18. Back To Top    #18

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    Re: CYA and FC?

    The loss from sunlight varies a lot based on the number of hours of direct sunlight on the pool, the time of year, and latitude. This post shows a table with some percentages where 50 ppm CYA would be around a 40% loss so having a roughly 50% loss at 45 ppm would not be completely out of line. This is why in very sunny areas some people run their pools with a higher CYA level, but of course that's a bit risky since if you do get the FC level too low and algae starts to grow it takes quite a bit more chlorine to shock the pool.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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