Testing pH, seems to rise after test tube sits a while, normal?

oldguy70

Silver Supporter
Jun 26, 2015
159
Glendale, AZ
#1
I always test pH first, I will leave it sit go on to test FC, then rince both tubes.....I always notice that the pH has risen say to 7.8 after initial test of 7.6 within just a couple of minutes....is this normal?