What should the pressure on the gauge be?

Every pool is different. Make sure that the pressure gauge works properly. It should return to zero when the pump is off. If your filter has one pressure gauge, make note of the system pressure after backwashing or cleaning your filter. Generally pressure changes of 6 to 8 lbs. indicate the need to backwash or clean the filter. If your filter has two pressure gauges, a pressure differential greater than 10 lbs. indicates the need to backwash. After backwashing the differential should be 5 lbs. or less.