Mike Otto had an article in the magazine a year or so ago about valves in the outlet pipe. IIRC he said that if they weren't opened and moved around once a year they tended to stay closed........


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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).