Chemical method of testing pool size?

[EarlTheCow]

I have a fairly irregularly-shaped pool that I'm getting into shape after buying our house (so far had to replace the pump and fix a huge outlet leak at the concrete line which was great fun). Since I've been replacing water due to the leak (and fixing the leak), I read zero CYA before adding four pounds of it (two the other day, and in the process of adding another two).

Is it possible to get an accurate estimation of pool water volume by checking the reading after completing the four pounds of CYA?

 

[JasonLion]

Welcome to TFP!

No, there is way too much uncertainty in the CYA test results to get a useful measurement. You can do better with chlorine, but even then the uncertainty in the reading is still fairly significant. By averaging measurements of a number of different chemical additions you can eventually zero in on the volume, but doing it with a single chemical addition is problematic.

 

[anonapersona]

Best to approximate as best you can geometrically, perhaps adding a little for pipe volumes. Then note how close you are on dosing chemicals by testing before and then an hour afterwards. Chlorine is not a decent thing to follow as algae can distort the measurements pretty quickly, but I gradually adjusted my pool volume estimate by noting the effect of acid additions, when TA was known. So if pH response is more or less than calculated, I adjusted my assumed pool volume until things agreed pretty well.

 

[EarlTheCow]

From this, I'm getting about 25k + maybe 1K for the spa. Sound plausible?

 

[anonapersona]

I will guess that this is perhaps low based on my pool which is similar shape but not 35' long but this is a real good start. Assuming you need to add acid to keep pH down, start with that volume and check the pH response after adding acid based on a current TA value. You can play with the Pool Calculator to see what pool size would have given you that response and try that volume the next time you adjust the pH. In two or three tries you will be getting the right answers from the pool to confirm your volume estimate. No need to be too exact, nearest 1000 gallons is fine.