Put a 5 gal bucket next to the pond that is filled to the brim. Put a vertical measuring stick in the pond. See if both drop at the same rate (inches per day). If not, then you have eliminated evaporation.

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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).