I have a well just for irrigation of lawn in which I have 18 zones with 9 heads in each zone.My well is 460' with a 1 3/4 hp pump and 20 gal bladder tank.Well produces 18- 20 gpm.My problem is my pressure drops to 30# and does not recover any pressure while sprinkers are on which is not enough to run sprinklers properly.Will a bigger tank help or am I looking in the wrong place? My pressure is set at 40-60.