Carolyn, today I called him. This winter is mild in Sochi. The day temperatures about 57.3F near the sea. In the mountains we have a little colder- around 44.5F and in the mountains at night it's down to little frost like 25F. So to ensure the fish breathing is simple by just crashing that thing ice crust which is formed during the night hours.
Extranjera, you were right, he uses the constant small water owerflow all the time.
We laught together on the matter of me starting building the pond. I said I do finally start next summer- so far to much travelling to visit all my houses.
