I worked some numbers and came up with a formula for chlorine demand. It's:
CD = 1 - deltadays_root(ppm_end / ppm_begin)
Where:
deltadays = the number of elapsed days
deltadays_root = take the nth, deltadays, root, so if deltadays was 2 it would be a square root, if 3 then cubed root, etc.
ppm_begin = starting ppm
ppm_end = ending ppm
I've cross checked the formula with a few points in the table (in this thread) and the numbers match up.
I was using excel to make the calculation and there isn't an nth root function available. You can use 1/del
