Your "normal" pressure is going to depend on too many factors to give you an exact number. Whatever your pressure is when you're in filter mode right after you backwash is your starting reference point.

DE is diatomaceous earth, which is a white powdery substance...it's a type of filter medium with a special filter, but many of us on this forum put a little bit in our sand filters to help with the filtration of the tiny particles a sand filter just won't get.