Quote Originally Posted by rkrgk View Post
But I think the math doesn't add up. 4.26 Gal of 6% bleach for 15K Gallons should add it up to ~24 ppm, correct? I think my pool is bigger than I thought. I think my pool could be 25K Gallons (which would make it approx 10ppm). I never got our pool info when we bought our house, I just assumed that it is just 15K.
PF = 8; 6% bleach contains ~0.5 chlorine gas equiv per gallon, so:

8 x 0.5 x 4.26 = 17 ppm

To calculate a kidney with fair accuracy, you need to following dimensions:
+ Maximum length
+ Minimum width
+ Small circle diameter (a kidney is usually laid out with 2 radius dimension)
+ Large circle diameter
+ Shallow end WATER depth
+ Deep end MAXIMUM water depth
+ Distance from extreme shallow end to break, along the max length axis.
+ Shape of deep end (straight down, bowl, angled hopper)
+ Which end is deep (small circle or large circle)
You can also measure it by adding 4 lbs of dichlor 55% available chlorine . . . AFTER your chlorine demand is gone . . . . and then testing both FC and CYA. But for now, you know your pool has a strong chlorine demand, and you don't know is causing the demand, so you can't estimate how fast you'll lose chlorine. It's entirely possible that you DID add 17 ppm of chlorine to your pool, but that 8 ppm was used up before you could test.