Pool math calculator & capacity

[Household6]

Does the capacity portion of the pool math calculator take into account slopes on the sides and from shallow to deep ends? And should I try to account for such?

We have a 40 x 20 concrete pool that's 9' in the deep end and 3.5' in shallow. The calculator shows this to be a capacity of 37,400 gallons.

However, when we refilled the pool after doing repairs, the water company's meter showed we only used 27,800 gallons. (Surely this is wrong, right?)

I'm attaching pics of the pool (before and during repairs, as the slopes are easier to see). I'm assuming the calculator does not account for slopes, and the water line runs about 4" from the top, so what capacity should we be using, inparticularly for SLAM?

And if we have been using 32k gallons, is this setting us up for failure? (It has only been a couple of days since we started SLAM. I'm just wondering if we need to go back to square 1.)

Thank you for any input.

 

[MarianParoo]

Divide your pool into sections. You have a rectangular area that is all 3.5'. You can calculate the volume of the remaining truncated "cone" if you estimate the radius/diameter of the deep end floor. You need to be sure you are measuring water depth, not wall depth, btw.

My volume (20x40x 3.5-8.5 with cut-outs in the corners and adding stairs) is 26,900 gallons. My calculation is way closer to the volume during fill. Pool math can't estimate slopes.

Just saw it is you, Household. One thread helps...

 

[Household6]

Ah! Sections! Brilliant!
Thank you.

I thought since this was a different subject, it belonged in a different place. No?

For what it's worth, I seem to have issue gaining input on questions with deep threads.

 

[YippeeSkippy]

As you add chemicals in based on Pool Math's projected amount retest 30 min after the addition and if the chemistry level is now exactly what you expected, you've got your pool volume figured out.
If the chemistry level is higher than expected, your pool is a bit smaller in volume. If the chem level is lower, your volume is greater.

At the bottom of PoolMath is a spot where (after inputing your 32k volume at the top of program) you can see the effect of adding <x> amount of <chemical> and it should give you <y> test result change.

 

[Household6]

As you add chemicals in based on Pool Math's projected amount retest 30 min after the addition and if the chemistry level is now exactly what you expected, you've got your pool volume figured out.
If the chemistry level is higher than expected, your pool is a bit smaller in volume. If the chem level is lower, your volume is greater.

At the bottom of PoolMath is a spot where (after inputing your 32k volume at the top of program) you can see the effect of adding <x> amount of <chemical> and it should give you <y> test result change.

Well duh! I've been playing with that bottom calculation for days. Why didn't I think of that?
Thanks Yippee!

 

[MarianParoo]

FYI: "Effects of adding" is better trusted with things like pH vs FC. Liquid chlorine can be stronger than labeled or weaker. I suggest doing your own math first and using the calc as confirmation. We are so dependent nowadays on computer programs to do our thinking for us!

 

[Agent99]

Looking at the shape of your pool bottom, I can see why Pool Math would estimate a higher volume that your meter showed. I think having the meter data is quite nice...now you know for sure! I would use the meter number to dose. See if it is accurate.

The way Pool Match calculates is to simply average your depth: (9+3.5)/2=6.25. Now 20*40*6.25=5000 ft^3 which is 37,402 gallons.

I also wouldn't be surprised if your depth isn't 9' and is less. The dosing of chemicals and their results will clue you in for sure and if you keep careful record, you'll hone in on the amount of water to use.