This is a first. After I backwash/recharge my DE filter the pressure has always run, for years, between 10 - 11 psi as long as it's clean. But now I've noticed that it's been down to 8 the last couple of days. I've recharged it, cleaned the baskets, checked the weir, all is clear. The return feels normal and I do not see any air bubbles, I'm stumped.