Do a search for pan evaporation rates thru NOAA for your area.

In your pond, that pump will only contribute slightly less than 1/8" of water per day. No pond is perfectly sealed, so you have leakage in addition to evaporation loss.

1' of water that covers one acre = 325851 gallons.

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).