On Mon, 30 Jul 2007 04:55:14 CST, chatnoir
wrote:

I usuallu just use a bottom filter that jets water upward in winter!
I live in Denver. Was cold enough to kill my zone 5 plants the last
two winters! They say such keeps there from being an insulating
layers of warm water in the bottom of the pond! Would like the Myth
Busters to test out that theory Since warm water would rise!

http://www.simetric.co.uk/si_water.htm

So would water near freezing temperatures, leaving a layer of water
close to 4C (39F), it being more dense.

Regards,

Hal