I have a small pond (8' x 5')that is only 22" deep, that in previous winters I have covered with a tarp and teepee style tubing. It has a de-icer in it. Worked well, however it needed careful monitoring to keep the snow off of it.
I was thinking of just leaving the cover off and only having a de-icer working to keep a small portion of the pond clear. Do I need a bubbler or anything to encourage water circulation - I plan on turning off the pump. Hate to lose the fish that are very happy in there for the past 5 years.
My pond is 5x5and1/2' and 24" deep. I use a pond deicer during the winter. It pretty much keeps most of the snow melted. Its not covered. I don't have fish. Lots of people here have mentioned keeping a bubbler going during winter, so I would use both if I were you. Last year I only used a deicer when it was really cold, and would turn it off and run the pump when it was above freezing. But last year I lost 3 frogs, and I think it was because of the fluctuating temperatures. So this year I'll just use the deicer and if I want to oxygenate the water, I'll run a different electrical line to the pump. Good luck to you.
I have the same size pond as catherinet, but in zone 4. I use a tank heater (turns on under 40F) and cover 2/3 of my pond with a sheet of styrofoam insulation across old 2" x 4"s (weighed down with a few rocks) to keep the windchill factor to a minimum. I turn my pump off but do use a small air stone - not sure if it really helps, but it makes me feel better! Haven't lost any fish since I started doing this.
I think with the pond that shallow you may need a little more then just the de-icer. The styrofoam that sheepco meantions is a good option. A pool solar cover can be used too. It floats on the water to help keep some warmth in and reduce evaporation. You need to keep about 1/3 of the pond uncovered for gas exchange if you use this.
I don't think a pond that is 22 inches into the ground will freeze solid. My pond is about a foot deeper, but I never had over 8 inches of ice in a decade of winters.
A heater should work fine, but the bubbles of an air pump will help bring toxic gas to the surface and provide a healthy environment for fish.
