Just replaced sand filter valve with pressure gauge installed; I didn't use a pressure gauge on the old valve. My questions is, since I can't find an answer with Hayward, what pressure reading should be showing? Mine is registering 19 psi after backwash; the inflow is strong. My sister told me hers always registers between 2 and 5; she has a lovely pool. Just wanting to make sure I'm okay. Also, at what psi should I backwash? Thanks.