Using acid to determine pool volume

Katodude

Silver Supporter
Aug 22, 2017
949
West Palm Beach/Florida
I have read the post about using TA to determine pool volume and was wondering if there was another way. My TA is not high enough to use the acid method listed, and I don't want to add baking soda to my pool, as I work really hard to keep the TA down. I will be installing a pH meter that has a resolution of +/- .001 and an accuracy of +/- .002. Is the strength of store bought acid consistent enough where I could use it to calculate volume by how it changes my pH? Is the accuracy of my meter enough to get a good measurement?

If possible it would be really nice since I can repeat this many times to ensure consistency. I can measure pH 100 times a day if I want (I know that adding acid multiple times a day is not a good idea). But I can very easily run the test once or twice a week and average the results.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,062
Tucson, AZ
It won't work as you expect it to. PoolMath, at best, only offers an approximation of what the actual pH value will be when acid is added to water because the pH change of highly complicated and buffered solution is a non-trivial problem in quantitative chemistry. When three buffering species are present (carbonates, cyanurates and borates) with a very high ionic strength solution, explicitly solving the mathematical equations for pH change is impossible. It becomes a problem of solving a complex array of multiple equations in multiple unknowns. There is computer software that can do it, but it's thousands of dollars per license per year typically and, even with that, you're still only going to get an approximate pH change.

This is why the chemical measurement of pool volume uses TA - adding one mole of acid consumes one mole of carbonate alkalinity exactly. Therefore, if you measure the alkalinity before and after, then you know the exact concentrations involved and you can calculate volumes.