pH popping up!?

Hi guys 🤗

As the title says:

I blend my water and organic liquid nutrients from Biobizz ( grow/bloom/calmag/topdress ) and pH regulated down to 6.2 in a container and start the airpump, 2 days later when I test the pH it says 7.9 🤷‍♂️ why is this happening? And should I just pH down just before use!?

Thanks for your time reading and commenting on my post, I appreciate your time and help a lot!!

Best regards The Organic Growth Dude! 🤩