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Thread: Shock process and funny numbers

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    Shock process and funny numbers

    Had some unusually high chlorine demand (for no apparent reason, but that's another issue) so started down the shock path. Mind you, through this entire process, CC has never been over 0.5.

    I lowered the pH to 7.2 or 7.1. First question - that's a good level to start with, right? Is it okay if I slightly overshot the pH lowering?

    Now, the numbers...When I do the math myself, 121oz jug of 8.25% bleach in my ~15,500 pool (mind you I'm 100% sure on the pool volume), I get that it should raise the FC by 5.03ppm. But the pool calculator says it should be 5.2. Does anything else affect the FC numbers?

    So, about that bleach...I measured the pool at a little over 6FC and, with my CYA at 50, the pool calculator says shock level would be 16. So I figure 2 bottles of the 8.25 to start and go from there. But after the 2nd bottle and letting it circulate (poured it slowly in front of jet, let pump run at full speed) for 30-45 minutes, the level I got was 21! I took my sample from the opposite end of the pool, but did I let it circulate long enough? And by overshooting so much, is that an issue?

    Regardless, we're off now, so I let it go over the day yesterday and check the level at night. It's all the way down at 14. So, using the pool calculator, 72 ounces of 8.25% bleach should raise me by 3.1, which will get me to 17, which should be good. But, after the same process (slowly pour in front of jet, let circulate for 30-45 minutes), my FC is all the way up to 21! Instead of raising it 3, it raised it 5! Huh?

    Okay, well, either way, it's at shock level, let it roll. I test it this morning and it's at 18.5. CC was 0.5 or 0 (honestly don't remember right this second), but a 2.5 drop in FC. I'm still over shock level, so I'm not adding any more bleach. But can anyone make sense of all this for me? I'm extremely confused about the above...
    15,400 gal, 16x32 vinyl rectangle (sport dig), Intelliflo VS, 240 sqft cartridge filter, Intellichlor IC40, Mastertemp 250, Dolphin supreme M4 cleaning, Pentair EasyTouch4

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    Mod Squad Bama Rambler's Avatar
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    Re: Shock process and funny numbers

    A lot of builders, pool stores, owners overestimate the volume of their pools a lot. That sounds like what's happened with you. Keep track of what you add and how much it affects the pool and over time you can adjust the volume to match the changes.
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    Re: Shock process and funny numbers

    There is no need to be that precise. 5.03 vs 5.2? Close enough in my book. How are you 100% sure of pool volume? It could be a few hundred gallons on either side of 15,500. Lot's of variables in a pool dig. 8.25% bleach could be a little stronger than that if it's fresh or a little weaker if it's been sitting around for a while. After you have been doing this for a while you will know that one jug raises the FC by x amount. Don't worry about the exact numbers. You sound like my son who has to have everything work out to a precise answer. He's studying to be an engineer. There are times when preciseness is needed but pool chemistry is not one of them.

    Was the 2.5 ppm drop in FC overnight with no sun on the pool? If so then you have something consuming the FC and need to continue with the shock process. What part of the country are you located. This heat we are experiencing can cause a larger FC loss than is normal. It sounds like you have a good grasp of what you need to do. Just trust your tests and do what the results tell you to do. Good luck.
    23x40 freeform w/spa, 28,000 gal. PCC-2000 in-floor cleaning. Pebble Sheen w/flagstone coping. 14' weeping wall, (2) 18" sheer descents. Sta Rite- cart 400 sqft. filter, Intellipro VS pump, 1hp (cleaning)2hp (water feature)Max E Pro's. Easy Touch 8 function w/IPod. Rainbow chlorinator, Paramount Clear O3 (I know, I know), Max-E-Therm 400K heater.

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    Re: Shock process and funny numbers

    I'm 100% sure of the volume because I know every dimension in the pool (I had it built) and I've calculated it out and modeled it multiple times. No one told me the gallons, I calculated them and the math otherwise has consistently reinforced the numbers. Yes, it could be little bit here or there (every inch the water is higher or lower is 319 gallons), but that's a 2% difference and in the grand scheme is close enough. The point is, there's no way I'm more than a few hundred gallons off.

    What I'm trying to do is understand why the numbers are so different. If I strictly had a 32x16 flat pool with no deep part (the shallow is 42 inches), I'd have over 13,000 gallons. These numbers are acting like the pool is only 10,000 gallons or like it's 12.5% bleach. Can there be that much fluctuation in bleach? It would degrade, not get stronger if it sat around.

    As far as the drop, no sunlight. And in southeastern Michigan it hasn't been that hot the last couple of days anyway.

    Yes, I'm continuing the shock process, but one thing I don't understand is why no CC if it's using up that much FC? Shouldn't I still be getting some CC showing up?
    15,400 gal, 16x32 vinyl rectangle (sport dig), Intelliflo VS, 240 sqft cartridge filter, Intellichlor IC40, Mastertemp 250, Dolphin supreme M4 cleaning, Pentair EasyTouch4

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    Re: Shock process and funny numbers

    Do you have a drawing/diagram you've made that we could use to double check you pool capacity calculations?
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    Re: Shock process and funny numbers

    Sometimes the bleach is made overstrength so that as it degrades sitting in warehouses and on shelves, it still meets the stated strength. I've had batches where it was WOW that FC is high!
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: Shock process and funny numbers

    Quote Originally Posted by Richard320
    Sometimes the bleach is made overstrength so that as it degrades sitting in warehouses and on shelves, it still meets the stated strength. I've had batches where it was WOW that FC is high!
    Thank you! That makes sense! Am I letting it circulate long enough before testing though? For liquids, is 30 minutes with pump running and decent rule of thumb?
    15,400 gal, 16x32 vinyl rectangle (sport dig), Intelliflo VS, 240 sqft cartridge filter, Intellichlor IC40, Mastertemp 250, Dolphin supreme M4 cleaning, Pentair EasyTouch4

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    Re: Shock process and funny numbers

    Quote Originally Posted by doncaruana
    Quote Originally Posted by Richard320
    Sometimes the bleach is made overstrength so that as it degrades sitting in warehouses and on shelves, it still meets the stated strength. I've had batches where it was WOW that FC is high!
    Thank you! That makes sense! Am I letting it circulate long enough before testing though? For liquids, is 30 minutes with pump running and decent rule of thumb?
    Should be. If there's any doubts, get in there with the brush and work your way around the walls. That will set up enough cross-currents to really get it dispersed. Especially if you use a wall whale. If I go down one side of my pool, a few seconds later I see an eruption of water on the opposite side.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: Shock process and funny numbers

    Quote Originally Posted by Richard320
    If there's any doubts, get in there with the brush and work your way around the walls. That will set up enough cross-currents to really get it dispersed. Especially if you use a wall whale. If I go down one side of my pool, a few seconds later I see an eruption of water on the opposite side.
    Yeah...I don't actually have a brush of any type, much less one that cool...Maybe that's one of my issues...

    Will that one work with my vinyl liner?
    15,400 gal, 16x32 vinyl rectangle (sport dig), Intelliflo VS, 240 sqft cartridge filter, Intellichlor IC40, Mastertemp 250, Dolphin supreme M4 cleaning, Pentair EasyTouch4

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    Richard320's Avatar
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    Re: Shock process and funny numbers

    Quote Originally Posted by doncaruana
    Quote Originally Posted by Richard320
    If there's any doubts, get in there with the brush and work your way around the walls. That will set up enough cross-currents to really get it dispersed. Especially if you use a wall whale. If I go down one side of my pool, a few seconds later I see an eruption of water on the opposite side.
    Yeah...I don't actually have a brush of any type, much less one that cool...Maybe that's one of my issues...

    Will that one work with my vinyl liner?
    Yep. It's got nylon bristles.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

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    Re: Shock process and funny numbers

    Quote Originally Posted by harleysilo
    Do you have a drawing/diagram you've made that we could use to double check you pool capacity calculations?
    Here's the final specs. I've tape-measured enough it to call it good enough at least for pool calculations. I could go into all the gory detail on the math, too, if anyone likes. Keep in mind, the water level is typically 6 inches from the top of the pool, so the water depth in the middle (deepest part) is ~5'6". And the corners are 2' radius rounded (negligible difference) and I have steps that are outside the outline, which would give it a few extra gallons, but not many, but at least offset the rounding on the corners. Going by all that, I get 15,439.79 gallons...give or take . So I just roll with 15,500 and often round to 16K in conversation.
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    15,400 gal, 16x32 vinyl rectangle (sport dig), Intelliflo VS, 240 sqft cartridge filter, Intellichlor IC40, Mastertemp 250, Dolphin supreme M4 cleaning, Pentair EasyTouch4

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