I've been trying to determine the sizes of a large kidney shaped pool (pool "A"). I have a similar pool at the site next door for which I do have data, so I thought I'd test calculation methods based on it. Here's what I got on that pool (pool "B"), and I can't figure it out.

According to the original engineer spec sheet from 1977, pool "B" is 37,480 I.Gallons (approximately 170,000L or 45,000 US Gal). [extra info - it specifies 1,020 sq ft surface area, 3 feet min to 9 feet max depth (although the depth at the main drains actually measures 9'8").] Measuring the pool and using typical calculations for kidney shaped pools, I came up with 160,000L. Reasonably close, but pool "A" has a different side wall profile which would add a lot more water despite a roughly similar surface area, and a different shape, having one flat side where pool "B"'s outer side is very round. The same calculations come out at about 180,000L.

So I thought I'd try the chemical method described on this site. I waited until my TA was low, tested with 10x accuracy and got 85. I added exactly 5kg of sodium bicarbonate (weighed with a kitchen scale), re-tested about an hour later and got 95. This gives me a result over 300,000L...? Curiously, I tested again the next day (using normal accuracy) and got 110. So perhaps the bicarb wasn't dispersed enough in the pool after one hour?

I'm confused at this point and considering completely draining the pools for next spring and filling with a water meter.