Up until last year I was using industrial air pumps, sometimes with heaters at the base of the air column on the bottom, to keep the surface open on my fish-bearing ponds during the winter. There was more water mixing than I really wanted, though, and it could be touch and go keeping the surface open in some weather.
Last year I put one of these in the front pond (I removed all the fish I could from the back one; the stragglers are on their own). There is a pump and heater in the column, and it constantly pumps water up in the tube to aerate it, using the heater to keep it from freezing in the top part.
With such a mild winter last year, it was hard to tell how well it really worked. This year we've had a lot colder temperatures and thicker ice, and so far the tube has constantly had water flowing in it, even with nights down to 3 degrees F. I guess I'll have to wait until spring to really know how well it does, after seeing how the fish overwinter.
The whole thing came practically disassembled (and I don't think it's supposed to--there's no assembly directions). I might have sent it back rather than figure out how to thread the tubes and wires, but it arrived the night before a hard freeze and I really wanted to use it. I looked at a lot of pictures online and guess I did an okay job of it, since it seems to work. I figure as long as water flows through the pipe and mixes with air it must be working, right?
I've tried a lot of things over the years, including floating heaters (very high failure rate, and the fish can't leave them alone), water pumps (too much water disturbance of the bottom, or they freeze over anyway), bubblers (it takes a LOT of air to keep the water open when it gets very cold). I know this question comes up periodically, but I'm always interested in what other people have learned about the subject.
