I use a submersible pump in pond to irrigate lawn the pump I was using was 3/4 hp 12gpm pump I was pumping at 500ft of 1in pipe with 40ft of elevation rise I was getting 15gpm with pump that was rated at 12gpm. The pump went bad and I replaced the pump with a 1hp pump rated at 25gpm but I checked it and I am only getting around 10gpm how could this be or what is wrong by the pump curve it should be around 28gpm at the elevation rise. what could cause this I was expecting to double my gpm.