ph test phenol red reads 7.2 then jumps to 7.5 !

i've been working on getting my pH down from 7.5

today when i measured, using bio-lab inc phenol red drops, the color matched the 7.2 orange. after about 45 seconds the color started creeping up. by 90 seconds it was about 7.4, after 120 seconds it was a bit above 7.5.

i double checked and it did the same thing.

my original question was this: which measurement do i use ?

but
i checked against some hth drops i have. it matched the 7.2 orange, and then stayed there.

just wondering what's going on.

my numbers:
CYA: 50
pH: 7.2 (i think. was 7.5 before applying pH down)
Alk: 90
Cal: 100
FC: 4.5
CC: 0

thanks in advance,
max

I would use the 7.2. Run the test, read it, then ignore any changes that happen after the fact. I have other tests that have done that in the past, too, and Ben always advised to read the immediate result and disregard any later changes.

Janet

excellent. thanks !
max