Real capacity of my pool?

Roberto

Active member
Jul 8, 2007
28
Central Texas
#1
Greetings, all,

I have an oval pool and I am in the middle of doing a Baquacil conversion. My pool is 15X30X4 and the manual that came with my SWG says to multiply L X W X D X 6.7, which comes out to 12060 gal.

The pool calculator comes out at 10600 gal, and the discrepancy in capacities makes a difference when trying to add chemicals in ounces, calculated according to its capacity.

Which one do I go with?

Thanks,
Roberto
 

duraleigh

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Apr 1, 2007
31,333
Sebring, Florida
#2
Roberto,

Split the difference. Then, adjust accordingly if your chemistry applications don't hit the target. It won't be that critical.
 

JasonLion

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May 7, 2007
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#3
If you didn't meter the water when filling the pool there is no way to know the number of gallons exactly. There are so many variables, curved corners, sloped bottom, differences in depth, measurement errors, and so on.

What really matters is measuring your levels after adding chemicals and adjusting from there to get to where you want to be. To start with add chemicals in portions lower than calculated, retest and add more. Over time you will get a sense of your pool and know that you need to go a little higher or a little lower then the calculator says. These differences from calculated amounts aren't only because of volume estimates. Purchased chemicals can be somewhat stronger or weaker than the nominal amount, other chemicals in the water and interact to change the effect from the expected one, and so on.
 

matt4x4

Well-known member
Apr 2, 2007
312
#4
I'm assuming its and oval pool 15x30x4 feet deep - flat bottom?
to get your cubic feet, do:
((pye x radius x radius) + (15x15))x3.5 feet deep (since you don't fill to the 4' mark)
((3.14x7.5x7.5)+(15x15))x3.5=1405.6875 cu ft
7.48052 is you multiplier to gallons

So you should have 10515.2735 gallons if you fill to 3.5 feet, adjust the 3.5 value according to actual depth of water (just measure top down to water level and subtract from 4 feet.).
 
#5
matt4x4 said:
I'm assuming its and oval pool 15x30x4 feet deep - flat bottom?
to get your cubic feet, do:
((pye x radius x radius) + (15x15))x3.5 feet deep (since you don't fill to the 4' mark)
((3.14x7.5x7.5)+(15x15))x3.5=1405.6875 cu ft
7.48052 is you multiplier to gallons

So you should have 10515.2735 gallons if you fill to 3.5 feet, adjust the 3.5 value according to actual depth of water (just measure top down to water level and subtract from 4 feet.).

You can't argue with math, but why does why does michael smith's bleach calc
show 15x30x3.5 @ 9276.75? I've got a 15x30x4 oval (3.5 at full) and I've been
using 9300 gal as my pool volume for testing, which never seems to measure out
just right. I would like to get as close as possible to the correct volume to alleviate
some of the guessing.

Just curious
Todd
 

JasonLion

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May 7, 2007
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Silver Spring, MD
#6
All of the calculators assume that your pool is a perfect rectangle, oval, or circle. No pool is a perfect shape, all of them have variations. Most of the calculators also do some rounding, Pool Calculator shows results to the nearest 100 gallons. Some of the calculators also approximate the multipliers, things like using 7.5 instead of 7.48052.

Inaccuracy in the volume calculation is only one of the factors that affects how much of each chemical you should use. Almost all pools vary in depth over time. Unless you have an auto leveler you water level can vary by a couple of inches, that can be hundreds or even thousands of gallons.The thing that really counts is getting experience with your pool. If you find that the calculator is consitantly low then use a high volume. If the calculator is consistantly high use a lower volume. This can happen even if you got the volume right in the first place.
 

matt4x4

Well-known member
Apr 2, 2007
312
#7
Actually, I believe the calculator actually takes into account that you will not fill a 4 foot pool all the way to 4 feet, so the height calculation likely removes 6" from the number you give the calculator since you are told to provide physical pool dimensions, not water dimensions....

Reason I'm thinking this is if you take Roberto's numbers for his pool, and plug them into the calculator, the number 10600 with 4 foot walls, is almost identical to my 10515 at a 3.5 foot water level.
Now if you plug in a 3.5 foot wall height, it'll likely remove 6" or .5 foot to give you actual volume of water calculated at 3 feet deep....and so on.
 
#8
matt4x4 said:
Actually, I believe the calculator actually takes into account that you will not fill a 4 foot pool all the way to 4 feet, so the height calculation likely removes 6" from the number you give the calculator since you are told to provide physical pool dimensions, not water dimensions....

Reason I'm thinking this is if you take Roberto's numbers for his pool, and plug them into the calculator, the number 10600 with 4 foot walls, is almost identical to my 10515 at a 3.5 foot water level.
Now if you plug in a 3.5 foot wall height, it'll likely remove 6" or .5 foot to give you actual volume of water calculated at 3 feet deep....and so on.
That makes sense! So my 15x30x48" (3.5 foot water level) would be closer to 10,500 than
9300 gal.... Thanks for info!

Todd
 

Roberto

Active member
Jul 8, 2007
28
Central Texas
#9
Real volume?

I see. Waaaay too many variables, so I will split the difference, and add chemicals on the lowside of whatever the requirement is until I get the hang of it.

Thank you all, a lot of good information.

Roberto
 
G
#10
If you want the most exacte measrements break the pool up into standard geometric shapes and add the volumes togehter. An oval pool with straight sides becomes a circular pool (each oval end is half the circle) and a rectangular pool that is the length of the pool minus the diameter of the circular ends so:
pi x( radius x radius) x depth x 7.5 gallons per cubic foot for the circular parts
and
lenth x width x depth x 7.5 gallons per cubic foot for the rectangular part

Plugging in the numbers
diameter = 15
radius =7.5
pi = 3.14
3.14 x (7.5 x 7.5) x 4 x 7.5 = 5298.75

length (minus the diameter of the rounded ends) = 15
width =15
depth =4
15 x 15 x 4 x 7.5 =6750

add the two together and you get
5298.75 + 6750 = 12048.8 or about 12000 gallons.

If the acutal water level is 3.5 feet then it works out to 10542.7 or about 10500 gallons.

I only used one decimal point because that is the accuracy of the conversion for gallons in a cubic foot that I used (7.5)
 

matt4x4

Well-known member
Apr 2, 2007
312
#11
Waterbear - that was the calculation I used WAY up near the top of this thread, (Cylinder + Rectangular prism) - might want to go back to your papers :wink: