Help a guy out with a ph mystery

K so lately I've been trying to really science up my grow skills and I'm running into a ph problem in my res and I'm not even doing true hydro! I've got raised soil beds that I'm hand watering with a pump and wand and I've been noticing something I'll mix my res (proper order to minimize covalant bonding)
Then ph I'll make sure my ph is holding for a few minutes before I start watering. When I'm done watering I'll check my ph in the res again and it's always wayyyy out of whack I phed to 6.5 today's and when I was done it was 7.3!!!
The worst is when i do fulvic, humic, b vitamin and calmag
conditions:
Using tap water ppm around 150 ph close to 7

Res size 1000 litres

Using a bubbler to recirculate and air-rate the water

Any help is appreciated I know I'm probably missing something big here

Beneficial Microbes & Silica ?

I'm testing extra water still in my res that has never seen soil. I mix my res and with out doing anything other than take volume out of it the ph sky rockets

Bubbling air through water raises the pH. Odd that it would happen so quickly though.