O.K. All ponds leak a little. Until it's filled, that's an unknown. Find your pond on the map
here. There's 325,851 gallons in an acre foot of water. In your pond (at 3/4 ac) each inch of evaporation = 20,366 gallons. So you can figure out how many gallons you will need to pump per year just to keep up with evaporation. Bigger is better when dealing with pumps, I'd rather pump for a shorter amount of time than have the pump running for a longer period of time.