We have a small ground water pond, maybe 1/5 of an acre. It is crazy how it seems to have a mind of its own when it comes to freezing over. Last winter we barely got a skin of ice, certainly nothing safe for ice skating. This week we have had temps around freezing and in the 20s overnight and have open water yet here and there. For me the layer of leaves on the bottom in the shallows helps insulate the ground heat. In addition I have to keep snow off the banks if I want the edges to freeze. Beyond the warmth of the water (and any ground water that comes in) you also have to freeze the ground solid a ways around the pond or there is too much heat trapped in the 'bowl' yet.

If ice skating is your goal then you would not want any type of bubbler or deicer. In a deep pond the fish should be fine as long as you try to keep the snow pack off the ice (which you would do anyway to allow for skating) They have a warm water zone to use just like in any other natural lake that doesn't have a bubbler. However newer ponds may not have vegetation started to provide some added oxygen. My pond has never been successful in growing vegetation but have not had any 'noticed' winter kill either and my pond has the challenge of being more shallow.