Major Difference Between Plan Volume and Chemical Additions Volume

[csmyrnos]

So we bought our house about two years ago. The house came with a sweet in-ground Pebble Tec pool that has an attached spiller over spa, a waterfall, and a beach entry. I was able to obtain a copy of the plans for when the pool was initially built and the specs said the pool was 22,000 gallons in volume. Ever since I took over care of the pool, I’ve been using pool math to monitor my test results and take care of chemical additions. In doing so, I’ve discovered that my pool volume is actually closer to 14,000 gallons. For example, I needed to raise my CH recently. I used 14,000 gallons as my volume in pool math, followed the recommended addition, and landed in the exact spot that I needed to be. I’m glad I figured this out before adding additional difficult-to-get-rid of chemicals (CYA, salt, etc).

Any idea why there would be such a big difference from the builder’s specs to what seems to be the actual volume? I could see a few thousand gallons either way but 22k to 14k is a huge difference. Thanks!

edit: Plans added

 

[mas985]

They probably just guessed at the volume. The shape and dimensions would indicate something much smaller than 22000 gallons.

 

[csmyrnos]

That’s kinda what I figured. I’m glad I did some homework on the true volume before adding chemicals based on the higher value. I‘m in the middle of a SWG conversion so I added a bunch of salt to my pool (based on the correct volume). Pretty excited to not have to deal with daily liquid chlorine and/or pucks any longer!

 

[RMcGirr83]

I got 17,280 (32 L x 16 AVG W x 4.5 AVG D x 7.5 G/cubic foot).

 

[Bama Rambler]

Builders and mfg's almost always over calculate the volume of their pools. One thing they pretty much all do is calculate it to the top of the coping/rail so right off the bat they're off several thousand gallons. They also use gross dimensions for length, width and height.

 

[csmyrnos]

Thanks for the replies... I’m in the process of adding salt to my pool for my SWG (installed today) and am using an electronic salt meter to monitor the levels. Doing this, I’m right around 17.5k gallons so Rich’s calculation seems just about spot on.