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Thread: Measuring pool volume during drain refill?

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    Measuring pool volume during drain refill?

    I've got a weird free form pool with spillover spa. I've heard a few wildly different estimates on volume and I'm going with 18000 right now.

    Is there anyway to meter the water going out when I drain so that i can get an exact amount?


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    14,000 gallon IG plaster pool, Cartridge Filter

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    East_Akl_Neil's Avatar
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    Apr 2012
    Auckland, New Zealand

    Re: Measuring pool volume during drain refill?

    While waiting for one of the other experts to come along, I'll put my 2c in.

    I cant see any reason you could not source a sutable size water meter and plum it in, however I expect that it would cost quite a bit. If you could hire/borrow that would be good.

    One other way is, depending on how you get fill water, is to read the water meter to your property, fill your pool by a set amount (e.g. 20-30mm, more the better as it gets more accurate) then read the water meter again. You then can calculate the pool volume with some accuracy
    Late 1970's 39000L IG Concrete Pool with Vinyl Liner
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    JasonLion's Avatar
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    May 2007
    Silver Spring, MD

    Re: Measuring pool volume during drain refill?

    Water flow meters are fairly easy to find. The inexpensive ones are significantly less reliable, but can still usually be gotten to work well enough to use once while filling a swimming pool.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Join Date
    Jan 2013
    League City, Texas (South of Houston)

    Re: Measuring pool volume during drain refill?

    Why couldn't you just read your City water meter before and after filling? Baths and laundry wouldn't throw off the results by that much...
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    Re: Measuring pool volume during drain refill?

    I did a drain and refill last year and read the city meter before and after. It took about 2 1/2 days. Ended up being around 23k gallons. I considered the amount used in the house basically negligible - a few hundred gallons at most.
    23,000 IG Plaster pool w/ spa, Pentair FNS Plus 48 DE Filter, Hayward RS1000 Main pump, Polaris booster pump, CPSC48 SWG, Legend pool sweep. Dallas, Texas, Full sun, Taylor K-2006

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    BoDarville's Avatar
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    Jun 2012
    DFW, Texas

    Re: Measuring pool volume during drain refill?


    Agree that water meter (in-line or city water meter) is the most accurate method and is my primary recommendation. With that said, here's some other options if the meter was either not used or read during the D&R:

    • 1. Here is a link to a pool volume calculator that shows examples for different shapes of pools: I would measure the pool and spa separately and then add the two volume figures from each to arrive at the total.

    • 2. Assuming your pool water is in good shape (a CC of 0.5 or less, no algae or other organics, and clear water) and you have a test kit with a FAS-DPD chlorine test (included in the recommended test kits) you can use the Pool Calculator (see link in my sig) as follows:
      [list:6o11tbug]a. Input your current volume estimate of 18,000 gallons along with the chlorine source and strength % (for example, bleach @ 8.25%). The chlorine input is located in the yellow-banded FC section of the Pool Calculator at the top of the page. Volume input is located in orange band just above FC section.
      b. Turn pump on and let run for at least 1/2 hour before proceeding to the next step.
      c. In the late afternoon or early evening, run a test for FC. Reason for running test at this time is to eliminate effect of sunlight on consuming chlorine.
      d. Record the current FC test results along with the desired target FC and input both in Pool Calculator
      e. Dose pool with the amount of chlorine calculated by the Pool Calculator to reach the desired target FC level and leave pump running.
      f. After 1/2 to 1 hour, retest the FC. If the new FC level is at the desired target level, then the volume estimate can be considered good. OTOH, if the new FC level is either higher or lower than the desired target, then you will need to adjust the pool volume estimate up or down. If this is the case, you may have to repeat this cycle several times to arrive at a good volume estimate.

    Note that the Pool Calculator also has a section for estimating pool volume towards the bottom of the page which may be easier to use than the link in Step 1 (or you can use both).[/list:u:6o11tbug]

    Using the Pool Calculator method is a good sanity check regardless of the method used to estimate volume. Since I have never done a total drain & refill on my pool, I used the link in step one above to estimate the total volume of my pool & spa and then input that estimate into the Pool Calculator. As it turned out, the estimate I came up with was spot-on.
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  7. Back To Top    #7

    Re: Measuring pool volume during drain refill?

    So for what it's worth. I was still going on 18000 gallons when I was buying salt to put back in. I only got 10 bags to play it safe in case I was wrong.

    Now my salt is at 4000 so I'm guessing 12000 gallons. Going to chuck the sump pump in tonight to drain a bit off...

    Sent from my iPhone using Tapatalk
    14,000 gallon IG plaster pool, Cartridge Filter

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    Mod Squad Bama Rambler's Avatar
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    Jun 2009
    SouthWest Alabama

    Re: Measuring pool volume during drain refill?

    Did you test the water for salt before you put any in? The reason I ask that is that is that you'd be surprised how much salt is in tap water. If you didn't test it before I wouldn't adjust the volume based on that.
    Dave J. TFP Moderator
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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Measuring pool volume during drain refill?

    I find it hard to believe you would have been that far off on the volume ... much more likely that the salt was not zero when you started.

    Salt is actually a pretty good way to estimate the volume if you have a before reading and an after reading.

    I just replaced most of my water recently and decided to measure the the salt ... found it to be ~600 ppm. Also realize that using any type of chlorine (bleach, pucks, etc) will be adding salt to the pool.
    Jason, TFP Moderator
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