Also, the thicker the ice and the more opaque it is, the less sunlight will penetrate the ice. In other words, if there's 12"-18" of ice that is very milky in color, I would err on the side of caution and fire up the compressor and open up the pond. I'd actually probably fire it up sooner than that, but just using that as an example. A couple dollars of electricity vs. the dollar amount of fish in the pond is a cheap insurance policy in my mind.

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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).