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Thread: Gallon Issue??

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    Gallon Issue??

    I'm certain that my fiberglass pool is at minimum 15'8" X 34"...it is pretty much rectangular, has at least an 8ft. deep end and 3ft. shallow end. The sides are sloping in the deep end. When I do my calculations on the pool calculator...I keep backing into the calculation that I have approx. a 15,300 gallon pool. Is there anyway this is possible?? I was at 12 FC and was trying to get to 15 (based on the assumption of a 22,400 gallon pool). When I added 1 gallon and 1 cup as directed and waited for an hour, my new reading was 16.5-17.00. The only way to reconcile that increase using the same amount of chemical was to lower my gallons to 15,300. Something doesn't seem right?? Surely the pool is larger and closer to 20,000 based on the measurments?

    Thanks,
    Alan

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    Mod Squad Bama Rambler's Avatar
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    Re: Gallon Issue??

    When I figure it I get about 18,000 gallons and if the corners are rounded and the slopes wider then it's certainly possible that it's close to 15,000 gallons. Water volume will fool you and most people have a tendency to over estimate it.
    Dave J. TFP Moderator
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    Re: Gallon Issue??

    If you told the pool calculator you were using 6% bleach for 22,400 gallons, I also get 1 gallon 1 cup.
    If you then added that much 10% bleach instead of 6%, I get an FC increase of 4.8 instead of 3.

    If it really was 6% bleach, the chems don't lie... in fact that's one of the usual ways to measure the volume of an irregularly shaped pool, add a known quantity of something that will be easy to measure (like bleach), and see how much effect it has.
    --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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    Richard320's Avatar
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    Re: Gallon Issue??

    I can think of a few things you may have forgotten to take into account.

    You might be measuring pool depth rather than water depth.
    The sides may slope more steeply than you think.
    The bottom may be flat in the shallow end and then slope rather than an even slope from end to end.
    You may have forgotten to deduct for things like steps and swim shelves. I have one that displaces about 900 gallons. There's 7.48 gallons in a cubic foot.

    And going the other way, there's some water in the lines and filter.
    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: Gallon Issue??

    I'm starting to either feel real dumb or real frustrated...or both. I know how to perform titration tests...I did them throughout college. Here's the deal...yesterday I backed into a calculation (using bleach) that determined that I had 17,000 gallons. I mean I was right on...I was able to produce an exact FC number using the recommended bleach at 17,000 gallons. This morning, after doing a test and determining my FC was 13.5, I added enough bleach to raise it to what I thought was 19. When I tested it 1.5 hours later, it was at 22.5. The calculator says that should happen with a 10,000 gallon pool. What is going on? Is there not a way to get an accurate volume measurement?? This is driving me crazy!!

    Thanks,
    Alan

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    Re: Gallon Issue??

    Where are you getting your bleach? The calculations are assuming a particular strength of the bleach you add, and if that varies somewhat, your results will be off.

    If you have a big bucket you test your bleach this way: Put 4 gallons water into the bucket. If you don't know it's chlorine-free (e.g. tap water), test the FC. Add 1/2 tsp bleach, mix thoroughly. Test FC again. If it's 6% bleach the FC should go up by 10.

    Or if you're more comfortable with metric, add 1ml bleach per 10L water, and the FC rise should equal the % hypochlorite.
    --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
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: Gallon Issue??

    Paulr,
    I get my bleach at Home Depot and the strength is 6.15%. I put 6.15% in the pool calculator for my calculations. Any other ideas to determine accurate volume?

    Thanks,
    Alan

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    Re: Gallon Issue??

    You are using the same test kit and reagents (and test personnel ) each time, so if you're getting different results from different attempts to measure volume with the bleach method, that leaves two distinct sources of error: The strength of the particular jug of bleach you're using, or measurement error on the part of the tester.

    There's an extent to which it doesn't really matter that much. You shoot for 19 and get 22, big deal. On the other hand, for myself I like to know, so I can sympathize if you do too. And you can just do what I did: (1) pick a number and use that for a while. (2) keep track of whether you consistently undershoot or overshoot. (3) if the difference is consistent, revise the volume number and repeat. You were using 22400 and always overshooting, so now you pick a smaller number and see how that goes for a while. Eventually it will converge on a number you can be happy with.
    --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
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: Gallon Issue??

    Paulr,
    I like your response...I'm a perfectionist and need someone to calm me down at times.

    Thanks,
    Alan

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    Re: Gallon Issue??

    OK...I'm very frustrated again. I tested FC at 7:00pm and it was 19. I wanted to raise it to 22 in my supposedly 17,000 gallon pool. The Pool Calculator called for 3 quarts and 1 cup. I used a measuring device that measured my 6.15% bleach from Home Depot very precisely. I checked again at 9:00 and IT WAS 26! That correlates to a 7,100 gallon pool which makes absolutely no sense. I made triple certain that the bottom of the meniscus was on 10mL both times. I'm lost and frankly don't have a clue! Does the size of the "heaping scoop" of powder matter? Is there any other way to determine my gallons...can I pay someone to come out and get close. I hate to consider this trouble free stuff when I obviously can't even tell you what size pool I have. I'm through venting for the evening!

    Thanks,
    Alan

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    frustratedpoolmom's Avatar
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    Re: Gallon Issue??

    Are you using the small scoop end to dispense the powder, or are you using the flat-handled end?
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
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    Re: Gallon Issue??

    I'm using the small scoop end.

    Alan

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    Re: Gallon Issue??

    It sounds to me like either your measuring cup is way off or that bleach is much stronger than it is labeled. Finding bleach as strong as 8% in bottles labeled as 6% is possible, though rare.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Gallon Issue??

    Based on this post, I was way under estimating how many gallons I am working with in my 18ft x 36ft rectangle pool. I don't even know how I originally came up with 24,500! I did 18x36x6x7.5=29,160 (width X length X average depth X one cubic ft of water = ) I just rounded up to 30,000 to compensate for the water in the lines & pump. Wow, looks like I gonna need a bigger supply of bleach!
    1.) 27,000 gallons
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    Re: Gallon Issue??

    Quote Originally Posted by alanrmeadows
    Does the size of the "heaping scoop" of powder matter?
    Taylor says to use two level scoops, which the TF100 simplifies to one heaping scoop. The precise amount of powder doesn't matter that much, as long as it's "enough." I'd say, don't skimp on the heap, but don't feel like it has to be as big as you can make it either.
    --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
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: Gallon Issue??

    Quote Originally Posted by frustratedpoolmom
    Are you using the small scoop end to dispense the powder, or are you using the flat-handled end?
    Ann, I think I'm the only one on this entire forum that has done that
    Lynn

    16x38 FG, 20,400G, 1HP/2sp Tristar pump, Hayward 425sq ft cart. filter, Pro Logic4, SWCG, 3 returns, 2 main drains, 1 skimmer, 4 Pentair deck jets, Hayward Phantom pressure cleaner/booster pump, TF-100 of course :-)orthofish-s-pool-build-finally-t13179.html

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    Richard320's Avatar
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    It happened to me, too!

    I added liquid Chlorine 2 evenings ago, enough to raise it to 17.

    I was expecting to see 14 or 15 this morning. I got 18!!

    Hmmmm. Never had that happen before, but it is fresh Chlorine, just bought about 3 days before. I'm thinking, "Maybe they under-rate the Chlorine to allow for deterioration?" I do the TA test, and instead of that red color, I end up with sort of a pale salmon color, so I'm guessing the Chlorine is, in fact, really high.

    The Chlorine sample is still sitting there. I dribble a little extra water in it, get a pink cloud. Swirl. It disappears. Curious... Add some more. Same thing. Now I'm wondering. So I dump, rinse, and repeat the test, but this time I swirl a long, long time. Now I get 17.

    I'm thinking I have been getting complacent and not mixing things well enough to allow things to react fully. That, and the fact that I'm inexact when measure the Chlorine; I just guesstimate by the level on the side of the jug. I could be off by a cup either way.
    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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    frustratedpoolmom's Avatar
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    Re: Gallon Issue??

    Quote Originally Posted by orthofish
    Quote Originally Posted by frustratedpoolmom
    Are you using the small scoop end to dispense the powder, or are you using the flat-handled end?
    Ann, I think I'm the only one on this entire forum that has done that
    No you're not...
    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: It happened to me, too!

    Quote Originally Posted by Richard320
    I'm thinking I have been getting complacent and not mixing things well enough to allow things to react fully.
    The FAS-DPD drops react pretty quickly but I think you still want to allow a second or two between drops. I've noticed even with the speed-stir the TA test takes a second or so to fully mix. putting in drops as fast as you can count might be overdoing it...
    --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
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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