My sand filter has been consistently at 12 psi all season. All of the sudden last week it dropped to 8 psi. I cleaned out the skimmer basket and pump basket and sprayed them with a hose. They're 100% clean, but it's still at 8 psi. I don't think anything could be lodged in the pipes because the baskets were in there the whole time and would have caught anything. There is no bubble in the pump basket, and the water pressure coming out of the returns seems good.
Those are all the things I know to test for. Any ideas what could be causing it or how to fix it? Could a backwash and rinse possibly solve a low pressure issue?