"Peter Breed" wrote in message
...

Hi Bill,
My pond is 2000L about 6ft long 4.5 wide and 4feet deep (3 feet
underground, 1 over). From what I read on various web pages the winter to
spring transition seems to go smoother if you keep the filter going all
winter. I've moved the pump and filter outlet to one corner of the pond so
there isn't too much water flow for the fish to struggle against, but the
water was still chilling, covering seems to have reversed that trend. I
guess removing most of the wind chill has allowed the residual heat in the
ground to take effect.
Peter

Mine is roughly 4*8, but with less than two feet of water. Keeping the
filter going is not an option here, too cold.

When I covered mine two years ago I never got any ice and the heater was
only 300 watts. So I expect keeping the wind off the water is a major
factor.