Ph readings

Hi peeps been floating about the site for a few weeks and thought I'd ask
my first question ....hear goes I'm using canna coco pro plus medium I'm adding canna a and b
PH 5.8 I don't use all feed in one go so next day I check ph in res and it has gone up is this normal
or is my meter bust?

You can check your meter in a liquid with a known ph. I use coca cola, cause I drink that shit like water, and I always have it around. It ph'es out at 2.5

Thanks pal����