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Thread: Question about shocking

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    Question about shocking

    I'm currently trying to rid my pool of a small algae issue and have a question about "shocking". My CYA is ~70-75 so according to the Pool Calculator my shock level is 20-21. When I bring the FC level up to 21 and it then drifts down into the 12-17 range during the day/night, am I still "shocking" the pool (just a little slower)? Or is all that time below shock level being wasted? At what FC level (relative to CYA) are you still gaining ground and killing algae? Or are you still gaining until it gets down below minimum FC levels?

    Thanks...
    Fortune favors the well prepared

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    Re: Question about shocking

    Whether you have a little algae or a totally green swamp, algae is algae. For shocking purposes, unless you bring your pool to a shock level of FC for your given CYA, you aren't shocking anymore. Best to bring it there and keep it there at 21 until your FC holds overnight. If your shock level is 21 and your FC falls to 17, you aren't shocking anymore.
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    Re: Question about shocking

    Thanks, I'll keep it bumped up.
    Fortune favors the well prepared

    The build...
    viewtopic.php?t=3974
    Freeform 24' x 38' IG gunite. 3 1/2' to 8' deep. 28,500 gallons. AutoPilot Total Control SWCG. Pentair Intelliflo VF. Pentair CCP520 cartridge filter. Colorlogic LED lights. Tahoe Blue Diamond Brite. 1200 sq ft stamped concrete deck.
    More details as they happen...

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    Re: Question about shocking

    The recommended shock levels are to get a reasonably fast killing and clearing of algae from the pool. If the level drops somewhat, but not too much, lower (say, no lower than half the shock level), the algae is still probably getting killed faster than it can reproduce, but it will take a lot longer and there could be pockets of algal clumps or biofilms where the algae will be able to grow faster than chlorine can kill it. It is best to MAINTAIN the higher shock level to get rid of the algae more quickly, yet still be safe for 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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    Re: Question about shocking

    Shouldn't your Shock Level be more like 28? Thats what the Chlorine/CYA Chart indicates for a CYA level of 70 - SWG and Non SWG.
    18,000 gal, 18x32 IGP, vinyl liner, 3 to 5.5ft depth. One inlet/skimmer (Aqua Genie), one main drain. Hayward Pro Series Sand Filter w/filtration rate of 20 GPM/FT, Two-Speed Pentair Whisperflo 1 HP pump, Natural Gas Hayward H200 pool heater, Aquabot T2 (200 Series) Robotic Pool Cleaner (my best friend), Automatic Electric Pool Cover (2nd best friend).

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    Re: Question about shocking

    Jason's pool calculator has it listed as 21 for a CYA of 75.

    The chlorine/CYA chart does have it higher at 28.

    Dunno???

    Anyone else???
    Fortune favors the well prepared

    The build...
    viewtopic.php?t=3974
    Freeform 24' x 38' IG gunite. 3 1/2' to 8' deep. 28,500 gallons. AutoPilot Total Control SWCG. Pentair Intelliflo VF. Pentair CCP520 cartridge filter. Colorlogic LED lights. Tahoe Blue Diamond Brite. 1200 sq ft stamped concrete deck.
    More details as they happen...

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    Re: Question about shocking

    Chemgeek's well thought reply is worth re-reading. It's not that something abrupt or magical happens at a certain shock level of, say, 21. The same thing happens almost as well @ 20 or 22. However, the same thing does not happen just as well @ 12ppm or 45ppm

    Too much FC is frequently bad and too little FC is almost always bad. Chemgeek and others have developed these numbers as markers which tell us approx. where we need to be.

    If you come across a situation where two numbers are fairly close for FC, you can feel pretty safe choosing the higher one because the process will proceed a little faster and you are still within a margin of safety.
    Dave S. - Forum owner
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