Low pressure after moving filter

[mas985]

First, your pump is a AG pump which requires a flooded suction. In other words, the pump must be below water level otherwise it may not prme properly and air will remain in the pump basket affecting flow rates. If the pump is below water level, it should prevent most of air problems although if there is still too much suction head, the pump could continue to draw in some air. You mentioned lowering the pump 8" but if the pump is 18" above water level, you need to drop it 20" or so. 18" lift is not that much and probably explains why it is working somewhat but the performance of the pump would most likely suffer.

Second, most of the head loss in a plumbing system is in the equipment and the fittings and the straight pieces of pipe add the least amount of head loss unless they are really long. So just changing the pipe won't yield all that much improvement.