I noticed the same thing when I started up the aerator back in June. I haven't seen any trout after that, even tho I shut it off. I fired it up again towards the end of July hoping to drive any remaining trout to the 25-30 gpm well water that I was putting in the pond, but I haven't seen any. My guess is that they're all dead.

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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).