Backwashing at a 5 psi rise is fine. In fact I do mine less than that unless I'm vacuuming a lot of junk. There is truth to the idea that the crummier the sand gets the better it filters but if I want better filtration I throw some DE in the thing. As I said above I still can't imagine high pressure due to dirt causing the problem. Anyone else want to chime in here with any ideas no matter how bizarre they may be?
Al