Can anyone tell me why we can't get enough water to flow from this pond? We're using 2 5000 gph pumps, but it flows real weak. I've looked over the design several times and can't see the issue. It is 1400 ft sq and has 3 falls. It sits 17 ft. above ground level. Depth is 3-4 ft. I don't recall what size the boxes were. That's a good Q. It was put in at the beginning of last season and we just got the call.