Should I be testing my nute water when feeding, my soil etc?

Trying to determine why I'm seeing stunted growth all of a sudden.

In a soil grow, when I feed, should I ph test the water with nutrients in it?
Would a 5 ph water being fed to a 7 ph soil bring the soil's ph down eventually?

lastly, what should one do if their water source has a too high or too low ph?

Yes you should test the pH, and yes giving it a lower pH will slowly bring down the pH of the soil and if your water source is too acidic or alkaline then use some pH up or down to get it where you want it