FC and pH test sensitivity as samples measured 8hrs apart had different values

[CMH-CVG]

Two Taylor 2006C samples taken 8hrs apart showed increase in FC and pH.

The night before it rained/stormed all night. I cleared debris and baskets and tested the water.
The FC 0.8 and pH 7.0 were low.
I was about to add both Pool bleach (2 gal) and increase the pH, however, I waited and did more pool cleaning, including 2.5hr Dolphin floor cleaning.

I retested the water and to my surprise the FC increase from 0.8 to 1.4 and the pH also increased from 7.0 to 7.6
Is this a meaningful increase, not quite 1 log difference?

I have mostly needed to add just Pool Bleach to keep the pool clear, and have found variation in pH go away over time or due to rain, as well as most of the other test values, with the exception of CYA which keeps bordering near 80.
Had I adjusted the pH in the morning, I probably would have surpassed the upper limit...when I retested it later in the day.

QUESTION: Is this normal behavior to see changes in retested levels, and likely why I read to add only 50% of the suggested correction amount and re-test?

7AM: Cleared debris, emptied the return baskets
8AM: FC 0.8, pH 7.0, TA 80, CH 360, CYA 60

1PM: Ran the Dolphin 2.5hrs to clear the floor, backwash/rinse
4PM: FC 1.4, pH 7.6, TA 80, CH 350, CYA 60

Thanks, Carlos

 

[ajw22]

What is your pump schedule?

With rain the water will stratify and the rain water on the top of the pool will have lower chemical values. It takes a while for after a heavy rain to mix the water well so the chemicals are homogenous.

Don’t be quick to check chemicals after a storm.