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Thread: Need help understanding the CYA chart

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    Need help understanding the CYA chart

    My best guess is that let's say I have a CYA level of 30, my minimum FC reading should be 3 and my target FC should ideally be 5? So what does the shock FC mean? Does it mean if I need to shock the pool, should my FC reading be 16? Would shocking temporarily raise it to 16 to kill any algae then recede down to normal levels?
    ~30,000 Gallon Free Form Pool; IG; Vinyl; DE Filter; Installed 2005

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    Re: Need help understanding the CYA chart

    Shocking is a process... pool-school/shocking_your_pool/ If your CYA is 30, then the shock value is 12 IF you need to shock it. If there are no apparent water problems and you can pass the OCLT pool-school/overnight_fc_test test then you shouldn't need to shock it. So, the minimum is a level you should not let the chlorine fall below, the target is an ideal. You may need to dose above the target in order to ensure that with the sun you never drop below the minimum. Going below the minimum is what allows bacteria and algae to get a foothold.

    I'm new at this too so this is to the best of my understanding! I'm sure those who have been at this longer will be along to confirm (or tell me I got it wrong )

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    Mod Squad woodyp's Avatar
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    Re: Need help understanding the CYA chart

    What BethyM said^^^^^^^^^^^
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    Richard320's Avatar
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    Re: Need help understanding the CYA chart

    Quote Originally Posted by pisstol27
    My best guess is that let's say I have a CYA level of 30, my minimum FC reading should be 3 and my target FC should ideally be 5? So what does the shock FC mean? Does it mean if I need to shock the pool, should my FC reading be 16? Would shocking temporarily raise it to 16 to kill any algae then recede down to normal levels?
    Minimum means just that - FC should never drop below. Target is subjective; you want to be above minimum with some room to spare. You'll lose FC to sunlight and stuff blowing in the pool, and people swimming. So, if you lose 3 ppm per day, you better set your target to at least 6. Or 7, to get a little more safety margin.

    Shock level is the point at which it kills algae faster than the algae can reproduce. Think of algae as pool yeast. The shock process means maintaining that shock level by adding chlorine frequently until you've killed all the algae and there's none left to reproduce.

    Try for more information.
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    Re: Need help understanding the CYA chart

    Thanks guys, that answers my questions. I will be buying the Leslie's pool kit tomorrow so I am eager to see what the readings say.
    ~30,000 Gallon Free Form Pool; IG; Vinyl; DE Filter; Installed 2005

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    Re: Need help understanding the CYA chart

    Be careful buying a kit at leslies....You do not want to buy the K-2005.

    You need a kit that contains the FAS/DPD chlorine test.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Need help understanding the CYA chart

    OK, I will make sure. thanks.
    ~30,000 Gallon Free Form Pool; IG; Vinyl; DE Filter; Installed 2005

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    linen's Avatar
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    Re: Need help understanding the CYA chart

    Yeah, the Leslies kit is confusing, it usually contains the DPD chlorine test, not the FAS-DPD test that you really want.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Need help understanding the CYA chart

    Quote Originally Posted by BethyM
    I'm new at this too so this is to the best of my understanding! I'm sure those who have been at this longer will be along to confirm (or tell me I got it wrong )
    Wow - that was fast, you sound like any one of the regulars!

    The only thing you left off was your test kit recommendation and where to buy it.


    Note: I treat the target as my minimum, but that's just me.
    Aaron
    [ Vogue Vectra 24' AG | Hard plumb: Hayward Power-Flo Matrix 1HP 2-speed, 27" sand filter & Pentair MiniMax 100 NG | Taylor K-2006 | Central IL ]
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    Re: Need help understanding the CYA chart

    Quote Originally Posted by Speedo
    Quote Originally Posted by BethyM
    I'm new at this too so this is to the best of my understanding! I'm sure those who have been at this longer will be along to confirm (or tell me I got it wrong )
    Wow - that was fast, you sound like any one of the regulars!

    The only thing you left off was your test kit recommendation and where to buy it.


    Note: I treat the target as my minimum, but that's just me.

    I thought the same thing about BethyM... but I have not been a regular here much longer.
    -- Guy --
    10K gallons in 21' Round 52 inch wall Aqualeader AG, Hayward Power Flow LX 1.5 HP pump motor, Hayward Perflex EC50AC DE filter w/Cellulose, Wide mouth skimmer, 2013 new Diver Dan (craigslist) to replace the faded old Hayward AquaBug. TF-100

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    Re: Need help understanding the CYA chart

    Quote Originally Posted by Richard320
    Shock level is the point at which it kills algae faster than the algae can reproduce.
    Just a minor point of clarification. The shock level is where chlorine kills even larger volumes of green algae faster than they can reproduce, significantly faster so that you get way ahead of the curve and kill off all the algae in a reasonable period of time, usually within some number of hours but certainly within a day. The pool will then be cloudy and need to be cleared of the dead algae through a combination of continued shocking with chlorine and filtration.

    The minimum chlorine level for the CYA level kills small amounts of green algae somewhat faster than it can reproduce so essentially prevents it from getting a foothold. If you dump in a bunch of algae or organics into the pool, you can overwhelm the chlorine in the pool having the FC drop (if not overall, then locally in some area of the pool) and algae could grow so the minimum is like a knife-edge and works for normal situations but if you anticipate something unusual to stress your pool, then raise your chlorine level in advance to give yourself some room. Unusual events would include putting a dirty cover on the pool, turning on a solar system for the first time during the season, getting a storm that blows in a lot of debris into the pool, having a very large pool party with people filling the pool (say, 1 person per 1000 gallons), etc.
    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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    Re: Need help understanding the CYA chart

    Quick follow up question, how long after adding bleach to the pool should I test it to see my current level? thanks!
    ~30,000 Gallon Free Form Pool; IG; Vinyl; DE Filter; Installed 2005

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    Re: Need help understanding the CYA chart

    Give bleach/liquid chlorine at least half an hour with the pump running before retesting.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Need help understanding the CYA chart

    For how long after adding bleach with the BBB method do I need to run the filter? I plan on adding it when I get home from work at 8:00, but by that time the filter has already ran for 8+ hours so I'm hoping not to have to run it a lot more.
    ~30,000 Gallon Free Form Pool; IG; Vinyl; DE Filter; Installed 2005

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    JasonLion's Avatar
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    Re: Need help understanding the CYA chart

    Same answer, at least half an hour pump run time after adding bleach before you turn the pump off.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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    Re: Need help understanding the CYA chart

    Thanks, that is good to know!
    ~30,000 Gallon Free Form Pool; IG; Vinyl; DE Filter; Installed 2005

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