Every pond is different, and it's better to let the fish tell you how much food they want. (whatever amount they will clean up in 15 minutes)

In my pond, feeding 2x day, 50# will last a month or slightly longer.

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).