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Thread: Shock with starting CYA of zero- test results

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    Shock with starting CYA of zero- test results

    I'm new to pool ownership and opening a pool that was not opened last year. There is a brown layer coating everything and there was a modest amount of leaves/pine needles and debris in the deep end.

    I spent time this weekend cleaning out the heavy stuff. So last night I began vacuuming the pool. I also began adding 84oz of stabilizer to bring the CYA up to a target of 30ppm. Only about a 1-1.5 lbs of the stabilizer has dissolved. I'm planning to only add 2/3 of the stabilizer and retest in a week.

    Test results yesterday: FC=0, CC=0, PH=7.5, TA=120 , CH=60, CYA=0 My plan is to raise CYA while shocking.

    I began shocking tonight. I set a target of 13ppm FC estimating a CYA of 20ppm, even though I know I'm not even close to that but a lower CyA will also lower shock level. ??

    I added 352oz of 12.5% L.C. at 7pm. At 1.5hrs the FC=6.5.

    I recalculated and added another 144oz L.C I continued vacuuming and then brushing the pool. The water is stirred up with quite a bit of small organic material suspended in the water, but I can see the murky bottom. The pump will be running 24/7.

    2hrs later my FC=8.0 and CC= 2.0. I seem to be having trouble raising the FC to 13ppm.

    Will this be even possible when the CYA is so low? Is the L.C. being consumed so quickly that I won't be able to raise and hold it until the cya is raised? What should shock be with CYA so low but raising?

    Perhaps the Note in the suggested levels of FC section of the Pool Calculator is trying to tell me something. What does it mean?

    Thanks
    21k gal, IG vinyl, 3/4hp pump, Hayward S-200 sand filter, 25gpm; TF100 test kit

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    Mod Squad jblizzle's Avatar
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    Re: Shock with starting CYA of zero- test results

    Usually you target the FC at the targeted CYA level. So if you have added enough CYA to get to 20ppm, then you would use that for the shock level, which is 10 ppm according Pool School.

    Until that is all dissolved you will lose a lot to the sun, but you are also likely attacking whatever is in the water.
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    BoDarville's Avatar
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    Re: Shock with starting CYA of zero- test results

    Quote Originally Posted by Lowarea
    I spent time this weekend cleaning out the heavy stuff.
    Doing this reduced your chlorine demand.

    As jblizzle stated, you will lost a lot of FC due to the sun. To compensate, you can concentrate testing / dosing at night with hourly testing beginning as soon as your pool is not in sunlight and continuing until right before you go to bed. Add supplemental doses of bleach to keep your FC at 10 ppm. The FC should stabilize as more organics are killed off.
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    Re: Shock with starting CYA of zero- test results

    Thanks.
    Tested FC=6.5 and CC=1.0 CYA=0 with about 2.5# stabilizer dissolved as of 5am.

    I'll continue trying to raise and maintain FC while the stabilizer dissolves. All the while vacuuming and scrubbing.

    It looked pretty good this morning but it's a clear sunny day today. I'll be stopping home at lunch time to add LC.
    21k gal, IG vinyl, 3/4hp pump, Hayward S-200 sand filter, 25gpm; TF100 test kit

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    Butterfly's Avatar
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    Re: Shock with starting CYA of zero- test results

    Don't waste your CYA reagent by testing before about a week . After it has dissolved, just 'assume' it is in the water and use that as your CYA level.
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