Your not going to alter the pH of the medium by simply pHing the feeding solution. Promix will hold a decent enough pH by the buffers it contains for 3 months give or take. Unless extreme over feeding or constant over watering occurs. The addition of dolomite lime and/or worm casting will improve the performance even more. Dont fall into the trap of pHing, especially up, in soil grows. It causes more harm than anything.
^^^THAT^^^
Get some dolomite lime and some perlite, Promix doesn't really have enough of either for a entire grow.
Add the lime @1cup/cf of mix before use, or, 2tbl/gallon of mix as a top dress if the plants are already in the pots.
Perlite is mostly an eyeball thing, but when it looks like there is too much, it's just right.
pH'ng water or any liquids is stoner science that just creates extra work. Liquids only affect soils pH as they are passing through. The soil will bring the liquids pH to match the soils in short order.
Starting a worm bin is the biggest thing you can do for your garden bar none. You can start a worm bin for less $$$ than what "quality" will cost.
Kelp MEAL and neem cake/meal are both game changers and should be at the top of the list for things to get, even if it's just 5lb bags.
BTW, dolomite lime at HD or Lowes is ~$4.50/40lb bag. Do NOT get hydrated, 'quick', or slaked lime, or anything that sounds similar. Dolomite lime is just ground up dolomitic limestone and will say so on the bag.
HTH
Wet