New Pool Owner Getting Started - How much water?!

[ronwell]

Total newb here. I bought a new home with a pool. The previous owner told me the pool held 40,000 gallons. I wanted to be sure of the volume so that I could make accurate chemical adjustments.

I used a couple of the pool volume calculators found on the web to find out if 40,000 gallons was even close to accurate. It didn't seem to be.

So, I set out to model the pool in Sketchup to get the true volume. Here's what I came up with:



I believe my 3d model to be very accurate. I took careful measurements of pool edges and depths and had no trouble transferring those into my Sketchup model.

Sketchup tells me that the volume of the object (which only represents the water contained in the pool) is 2998.4 cubic feet, which is about 22,429.2 gallons. THAT'S NEARLY HALF OF THE VOLUME THAT THE PREVIOUS OWNER THOUGHT IT TO BE!

My question to all you professionals:

Are there any gotchas in my approach to figuring the volume? Should I and how do I account for water in the filtration system? Am I being too anal about this?

Thanks!

 

[JVTrain]

The best way to figure out the volume definitively is by using chemical additions to do so. It is important to have a good estimate of pool volume at least within about 1000 gallons for a large pool.

In a clean, algae free pool, using the FC level is a good way to get an estimate of volume. Using Pool Math and your best guess at pool volume, calculate what dose will raise your FC by 5 ppm. At night, measure your FC, then add that dosage. Circulate for 30 minutes and test FC again. Did you get the 5 ppm increase exactly? More? Less? Use that ratio of actual:expected result to adjust your pool volume estimate. Repeating again with your new estimate will get you even closer or confirm that you're very close.

You can also use CYA or CH additions in the same way, but not all pools need to have those added based on current levels.

Also... Welcome to TFP!

We like persnickety people around here so no worries!

 

[RobbieH]

The best way to figure out the volume definitively is by using chemical additions to do so.

This is exactly how I got to the final estimate for my pool.