Backyard Aquaponics
A place to discuss aquaponics

I've been comparing the efficiencies and wattages of a whole stack of pumps. From my calcs it seems that in the majority of cases running a smaller pump longer is more efficient than running a larger pumper for a shorter length of time. Also due to the extra power drawn when a pump starts running using an even smaller pump continously would use less energy again.

The most efficient pumps are the axial flow ones, but these are rarely available. I've been thinking for some time about making one using a RC sub propellor in a PVC tube; but there are a few details that would need to be solved: optimal spacing around tips to minimised drag; suitable thrust bearing; optimising head for given speed. Cavitation will be a problem too. There was an article in renew a while back about a super efficient natural swiming pool system that used such a pump (clever idea was to run the pump tube vertically, avoiding the need for a seal), but the head in that would have been a few cm at most.

mythbusters had a large scale one built out of an outboard motor in a steel pipe - they were pumping maybe 100L/s up 5 m. (5kW)

The reason we should be looking at axial flow rather than impellor based designs is because we are after large volume low head rather than low volume large head.