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Thread: Pool volume discovery

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    Pool volume discovery

    My pool is a 16' x 32' IG with vinyl liner. It has a 3.5' shallow end and an 8' hopper bottom deep end. Every pool calculator I have ever used shows it to be 21,200 gallons based on average depth, but I have always wondered if it was actually that high since there doesn't seem to be an easy way to take the hopper bottom slopes out of the equation. I had been dosing my pool based on the 21,200 gallon number, with .75 gal of 6% bleach giving me 2.1 ppm of FC.

    Last week I shocked to what I calculated should be 12 ppm, and the next morning when tested I found out I was actually closer to 15 ppm. I assumed either the bleach was stronger than 6% or I have less water capacity than I thought. Well, over the weekend I was digging for some paperwork and came across the original manual that must have came with the pool when it was installed by previous owners. In it it had a chart showing water capacity for their various sized pools, and my pool is listed at 18,350 gallons, or about 13.5% less than the calculators show.

    Not a bunch, but I thought I'd let others know in case they were wondering as well

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    Mod Squad JohnT's Avatar
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    Been there, done that. My installer told me my pool was 15,000 gallons bigger than it actually was. Rough figuring in my head showed him off by at least 11,000 gallons. I locked up the starter chemicals in the garage so he wouldn't add anything.
    TFP Moderator
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    I figured mine out by measuring the chlorine levels (no CC present), adding a precise amount of cal hypo (100 grams of 65%), letting it mix well and measuring it again, all done in the evening of course. (Must say the pool has 50 ppm borates in there too).

    The pool grew from 26k liters to a bit over 28k.

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    tagprod's Avatar
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    Quote Originally Posted by CaOCl2
    I figured mine out by measuring the chlorine levels (no CC present), adding a precise amount of cal hypo (100 grams of 65%), letting it mix well and measuring it again, all done in the evening of course. (Must say the pool has 50 ppm borates in there too).

    The pool grew from 26k liters to a bit over 28k.
    That's my plan with some pool salt. I'm going to add and see how much my ppm goes up and then break out some algebra to figure volume.
    Brian
    20K IG Gunite w/ raised 7ft spillover spa. 1.5 HP Hayward Northstar pump 425 sq ft Hayward cartridge filter, Colorlogic lights AquaRite SWG AquaLogic PS-8 control
    1hp pump for sheer descent

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    Quote Originally Posted by tagprod
    Quote Originally Posted by CaOCl2
    I figured mine out by measuring the chlorine levels (no CC present), adding a precise amount of cal hypo (100 grams of 65%), letting it mix well and measuring it again, all done in the evening of course. (Must say the pool has 50 ppm borates in there too).

    The pool grew from 26k liters to a bit over 28k.
    That's my plan with some pool salt. I'm going to add and see how much my ppm goes up and then break out some algebra to figure volume.
    Right on! It's an interesting exercise. I used DPD/FAS for the chlorine test (0.2 ppm precision). Depending on your salt test manufacturer the precision may only be 200 ppm (I know Taylor's salt test is 200 ppm per drop) and this may skew the calculation a bit.

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    tagprod's Avatar
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    Quote Originally Posted by CaOCl2
    Quote Originally Posted by tagprod
    Quote Originally Posted by CaOCl2
    I figured mine out by measuring the chlorine levels (no CC present), adding a precise amount of cal hypo (100 grams of 65%), letting it mix well and measuring it again, all done in the evening of course. (Must say the pool has 50 ppm borates in there too).

    The pool grew from 26k liters to a bit over 28k.
    That's my plan with some pool salt. I'm going to add and see how much my ppm goes up and then break out some algebra to figure volume.
    Right on! It's an interesting exercise. I used DPD/FAS for the chlorine test (0.2 ppm precision). Depending on your salt test manufacturer the precision may only be 200 ppm (I know Taylor's salt test is 200 ppm per drop) and this may skew the calculation a bit.
    I'm gonna have to rely on the readout from my remote for that. It's usually pretty accurate - when I've taken pool water to the pool store to be tested their test mirrors my readout. I don't do it often (take water to be tested) but I'f I'm out of CYA reagent I let 'em do it when I go in.
    Brian
    20K IG Gunite w/ raised 7ft spillover spa. 1.5 HP Hayward Northstar pump 425 sq ft Hayward cartridge filter, Colorlogic lights AquaRite SWG AquaLogic PS-8 control
    1hp pump for sheer descent

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