BleachCalc numbers don't match my chlorine increase???

[tcm]

Ok, last night we started using bleach instead of the cal hypo to chlorinate. My FC level prior to adding bleach was 3.0, I added 2.5gal of 6% clorox to pool last night after dark. This morning the FC is 8ppm. According to BleachCalc it should be at 6ppm for my size pool. I realize that the 52000 gal is just a estimate based on average depth for the pool, but to have increased 5ppm to 8. it says my pool volume would have to be 30000 gallons. The pool is 24' x 48', 4' to 8' deep has a set of stairs in one corner of the shallow end and a swim out ledge in both corners of the deep end. this may account for 1 ot 2 thousand gallons at most. Am I missing something here??

My Current numbers are:

PH - 7.5
FC - 8
CC - 0
CYA - 60
TA - 90
CH - 200

 

[JasonLion]

It is very likely that your pool is noticeably smaller than 52,000 gallons, though it seems unlikely that it could be as small as 30,000 gallons. I would guess at something closer to 40,000. There are a couple of ways to approach this. The simplest is to take this as a hint that the pool is smaller than you thought, and to continue watching other chemical additions to see what they do, adjusting your size estimate down over time if all/most of your chemical additions behave similarly.

Another approach is to do some additional measuring. How long is the shallow end, how long is the slope between shallow and deep, how long is the deep end. Are the corners fairly square, or are they rounded? Do the walls go straight down, or are they sloped anywhere? And so on.

 

[HarryH3]

When we bought our place, the previous owners (who had the pool built!) told us it was a 35,000 gallon pool. But my chemical additions always seemed to fall far short of the expected result. Then one spring I drained and cleaned the pool and then measured the water it took to fill it back up. It came in at 24,000 gallons, not 35,000.

 

[mynewpool]

I have the same issue as well. I use the calculator and the few times I have tested right after addition of bleach, it goes higher than expected. So I just let it go and maybe the next day I am good to go without having to worry about doing much.