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Thread: Pool Size Help

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    Pool Size Help

    Attachment 37527Attachment 37527I am trying to figure out how many gallons my pool is. It is somewhat irregular shape. The pool was built in 1987 and here is a copy of the plans. It is 3-6 feet. It has a connected spa as well. I am guessing like 20,000 to 25,000. Any help guessing the number of gallons?

    Dropbox - 05-24-2015 10-34 PM.pdf
    Attached Images Attached Images
    Last edited by Sir Thomas Hobbes; 06-02-2015 at 08:46 PM. Reason: add another photo
    20k? gal, IG plaster, 3HP Pentair Intelliflo variable pump, Hayward cartridge filter, built in 1987 with spa but currently have no heater.

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    Re: Pool Size Help

    Your pdf wont open. You can go here and estimate the square footage and let us know what it says.
    Area Calculator - Outline a property on a google map and find its area
    16k AG Vinyl Sand Filter

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    Re: Pool Size Help

    I uploaded an attachment. That google tool seems to indicate that the pool surface (excluding the spa) is about 562 sq ft. If I understand correctly the pool is an average depth of (3+6)/2=4.5. It seems that some online sources suggest a pool multiplier of 7.5 for a rectangular pool. If I can understand it then it would be 562 x 4.5 x 7.5= 18,967.5 gallons plus the spa. Does that seem right?
    20k? gal, IG plaster, 3HP Pentair Intelliflo variable pump, Hayward cartridge filter, built in 1987 with spa but currently have no heater.

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    BoDarville's Avatar
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    Re: Pool Size Help

    Welcome to TFP!

    Yes, that's definitely an irregular shape. If you really wanted to figure out the volume using a pool volume calculator tool, you would need to measure the pool in rectangular sections and measure each of those. In all likelihood, you would still have some irregular shapes left over. The good news is, there's a better way by using the Pool Math tool along with your daily dose of liquid chlorine.

    For now, assume your pool is 25,000 gallons. Enter this in the Size cell of PoolMath located at the top of the page.
    1. Perform a chlorine (FC) test using a FAS-DPD chlorine test and note the results. Enter results into the "Now" column of the FC section of PoolMath.
    2. Enter the target FC in the Target column of the FC section. PoolMath will tell you how much chlorine needs to be added to reach your target FC - note this amount.
    3. Be sure to note the % concentration of the bleach you are using and make sure this is entered into PoolMath.
    4. Make sure the bleach you are using is fresh.


    Add the amount of liquid bleach that PoolMath tells you to enter and let the pump run for an hour. Then rerun your FC test and record this result. FC should be at the target level. If the FC is less than your target, then your pool is larger than you estimated. If FC is greater than your target, then your pool is smaller than estimated.

    Using your second FC test result, you can interpolate your pool volume by changing the Size (in gallons) in PoolMath by using the following example: Assume your starting FC was 3 and your target was 5 and you were using 8.25% bleach. PoolMath would have told you to add 74 oz of bleach. Although you added 74 oz of 8.25% bleach, your second FC test is showing 6 ppm. Here's how you would do the interpolation:
    1. Adjust your target FC in PoolMath to 6 but leave the starting amount at 3. Leave everything else as-is.
    2. Adjust the size from 25,000 gallons to a lesser amount until the amount of 8.25% liquid bleach to add reads 74 oz. When this happens, note the size volume entered (in this example, the new water volume is 16,700 gallons).
    This new size amount is a very good estimate of your pool's water volume. Use the new size volume for your next dosing of the pool.
    Note: If your second FC test was less than your target, you would adjust the water volume up to a larger amount. Just be sure to enter the results of your second FC test as the Target before adjusting the water volume amount.

    BTW, when adding bleach or any form of chlorine, it would be best to do this either in the early morning or evening when no sun is hitting the pool in order to obtain the most accurate results. This removes normal FC loss due to sunlight, although the loss in one hour would likely be negligible.

    You can re-do this process on subsequent additions if you want to fine-tune this estimate and/or test it when adding other chemicals to go from your current to target amounts. Note that your water volume estimate doesn't have to be exact right down to the last gallon. Using this method with a good test kit and fresh chemicals you will arrive at a good-enough water volume estimate for managing your pool.
    Gold Supporter, TFP Lifetime Supporter, 26,680 gal Plaster IGP 3.5 - 10' depth / Attached Waterfall Spa, Manually Chlorinated, Triton Sand Filter, 1.5 HP * 1.1 SF = 1.65 SFHP 1-speed Pentair WhisperFlo WF-26 Pump, 400K BTU NG Teledyne Laars Series One Heater, Polaris 360, Test Kit Comparison, Chlorine/CYA Chart, SLAMing Your Pool, OCLT
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    Mod Squad JVTrain's Avatar
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    Re: Pool Size Help



    Also, when in doubt and you need to address an issue with adding chemicals, estimating a lower volume is safer.
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
    40x20 Pool: 32K Gallons * Vinyl * Bleach Chlorination * Hayward S270T Sand Filter * Pentair SuperFlo 1 HP * Teledyne/Laars Heater * AquaVac Tigershark * TF-100 w/ SpeedStir
    Isolated Spa - 345 Gallons

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    Re: Pool Size Help

    Quote Originally Posted by Sir Thomas Hobbes View Post
    I uploaded an attachment. That google tool seems to indicate that the pool surface (excluding the spa) is about 562 sq ft. If I understand correctly the pool is an average depth of (3+6)/2=4.5. It seems that some online sources suggest a pool multiplier of 7.5 for a rectangular pool. If I can understand it then it would be 562 x 4.5 x 7.5= 18,967.5 gallons plus the spa. Does that seem right?
    That's correct. When I measure my pool with it, I get 15640 gallons. My pool is actually 16100 gallons so there is some inaccuracy but being 3% off isn't going to affect much. I believe I would call it 20,000 gallons and then see if the dosages from PoolMath match up with it.
    16k AG Vinyl Sand Filter

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