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Thread: How many gallons is my pool

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    How many gallons is my pool

    I have a 16 X 32 inground pool. The deep end is 6' and the shallow 3'. According to the calculators, it should be 17,200 gallons. But in the process of adding salt, things don't add up...I've put in 8 40# bags, and had the water tested at 3000ppm.......By using the pool calculator backwards, that would lead me to believe my pool is only 13,000 gallons......

    Is it possible to b that far off, or is there something i'm not seeing.....
    17,200 in ground Vinyl pool......
    Salt Water
    Sand Filter

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    Re: How many gallons is my pool

    A pool 16x32 and 3' deep (no deep end) would be 11,500 gal. If the deep end is noticeably smaller than the shallow end the 17K number would be too generous. 13K seems a bit on the low side still, but...

    Pool capacity is always a matter of guess-and-check anyway. You currently have two data points. After a few more you'll settle on a number that works for you. (Took me 3 tries to come up with a number that worked for me.)
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
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    frustratedpoolmom's Avatar
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    Re: How many gallons is my pool

    Did you test the salt level before adding?
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
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    Re: How many gallons is my pool

    no
    17,200 in ground Vinyl pool......
    Salt Water
    Sand Filter

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    mas985's Avatar
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    Re: How many gallons is my pool

    17k would be for a pool that was a perfect rectangular box. Steps, curves, non-linear bottom all will reduce the volume. What is the shape of your pool?

    Also, you mentioned you had the water tested? Pool stores are often way off in their mesurements so you really can't go by that.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    frustratedpoolmom's Avatar
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    Re: How many gallons is my pool

    Quote Originally Posted by Wild Duk
    no
    Pools usually have a salt level already - even before manually adding bags of salt. It's always a good idea to test it before calculating the needed amounts. That could be throwing off your math for figuring the size....
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    Re: How many gallons is my pool

    Howdy Wild Duk.

    Did your friendly pool store employee use a beige cylindrical electronic meter when testing your salt levels? Also, was he incredibly charming and good looking?

    If you answered yes to both of these questions, then the salt reading is accurate. Many of the chemicals that you've used in your pool in the past may have added salt - it's not uncommon to see 800ppm or so in non-SWG pools.

    For you experts, would another 80 lbs of salt (putting him at between 3200-3300 ppm) and another retest with the same meter be enough data, or is that too small of a change? The electronic meter will not have been recalibrated in the meanwhile.

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    JasonLion's Avatar
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    Re: How many gallons is my pool

    Even the best salt meters don't have the precision required to determine the pool size from a single 80 lb bag of salt.

    The salt level would never have been zero to start. It could have been anywhere from about 300 to 1,800, depending on how much water has been replaced recently (and in the past).

    All we can really conclude is that the pool is somewhat larger than 13,000 gallons.
    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: How many gallons is my pool

    I was lucky since my pool was empty before opening I recorded my water meter reading before starting the fill and at stop points. I had a gestimatation of 16,000 gallons and was pretty close to my estimation upon filling.
    30 y/o 16,000 Gal free form IG by Anthony & Sylvan
    48 sq/ft Hayward Pro DE filter
    1.5hp super pump

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    mas985's Avatar
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    Re: How many gallons is my pool

    The other problem with TDS meters is that they measure TDS which includes salt, calcium, magnesium and any other dissolved solids. The assumption is usually that the other elements are small and don't contribute much to the total.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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    Re: How many gallons is my pool

    Even the best salt meters don't have the precision required to determine the pool size from a single 80 lb bag of salt.
    The other problem with TDS meters is that they measure TDS which includes salt, calcium, magnesium and any other dissolved solids. The assumption is usually that the other elements are small and don't contribute much to the total.
    Ah, okay. I figured that 80 lbs wouldn't be near enough, but I didn't even know that the meter was measuring anything other than salt, and I use the thing every day. Does this mean that it would be beneficial to overshoot on salt when using the meter to gauge how much to add? Or do the manufacturers account for the other dissolved solids when they decide on the ideal ppm?

    Does the salt control panel measure TDS also, or do they actually measure salt content?

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    mas985's Avatar
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    Re: How many gallons is my pool

    Despite popular opinion, I rely upon the SWG to tell me what the salt level is (actually its amps). The reason is quite simple, the SWG will turn itself off it the amps are too high or too low. So by relying upon the SWG to tell you salt level, you are really letting it tell you what is right. I use salt strips and a drop kit as well but it really doesn’t matter what those read. It may be useful as a life test for the SWG since the salt reading error does tend to increase with age. But bottom line, what the SWG thinks is very important and what the actual salt level is is less important.

    Personally, I target the low end of the SWG range but that is to reduce the false high salt errors when very hot water travels through the SWG after solar is turned on. Amps increase with water temperature and if the salt level is too high, hot water can trigger an alarm.

    While it is true that an SWG will produce more chlorine at higher salt levels, this does not mean that the life of the SWG is extended with higher salt levels. SWG life is usually measured in amp-hours. With higher salt levels, the amps increase and chlorine production increases in proportion to the salt level so the run time can decrease by the same amount (visa versa for lower salt levels). So in reality, the life of the cell should be nearly the same with high or low salt level as long as the levels are within range of the SWG operating parameters.

    As a SWG ages, you will find more salt is required to prevent low salt errors at which point it is a warning that the cell is about to die and you need to start shopping for a cell.

    So long story short, I don’t think it matters much what the salt level is as long as the SWG thinks it is within normal operating range.

    Also, forgot to add that yes, a SWG is a TDS meter. However, some offset the TDS measurement to account for typical levels of other solids.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

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