How big is the tank?
Do you know the exact number the pH surged to?
How often do you check pH?
Do you have gravel/substrate in your tank? If so, what is it?
Answering your first question: This depends on if your tank is established or not. If it is a well established, filtered tank, I generally check my pH once every other day at the same time (for example 2pm). If you have a smaller, uncycled tank that requires more water changes, then you should be checking it more often in my opinion (again at around the same time).
Answering your second question: Depending on how much it "surged by", it could be many things. If it went from say 7.3 to 8.2 in the span of a few hours, then there is something seriously wrong somewhere. If it went from 7.3 to 8.0 in the span of a week, then it's not as hazardous as the first example.