6 feet will put most of the pond below the freezing line. That has to give you more options. Should be feasible to keep the lower half above 45 with reasonable heating even if it gets to zero (in one of those record years) and certainly if the average low is above 15.
Ya. I'm planning on testing summer temperatures of the water to see if I could add a sturgeon down the road sometime. Of course i would have to get rid of the koi I'll have Inevitably stocked the pond with. Maybe I could do something good for the community and donate some of my unwanted koi to places that have large enough ponds. Maybe a church or nursing home so I could have the fish I want in my pond and others could enjoy some of the others as well
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