This is no doubt a 101 question, sorry. My pool was installed just last year. The pressure always used to go back down to about 13 PSI when I'd backwash. This year, I can't get it below about 18 PSI. Is this normal? I assume there's junk in there I can't get out with backwashing; just want to be sure. Today I ran the backwash longer than usual (several minutes), and turned the pump off/on several times to try jarring junk free. Still at ~18 PSI.