I am in 7b and therefore have no experience with 6a conditions. However, I know that there are ponders in the colder areas that don't seem to use heaters or deicers. For example, cliffandjoann are somewhere in New York and they have explained their setup in detail. As I recall, they have never mentioned a deicer. My impression is that more northerly ponders have deeper pond sections. Of course, you are already at 3' and that is usually considered a good depth. But if you could make one area deeper, it might help.

I have had success for years with an air pump and air stone set-up. Buy a more expensive pump, for long life, with two outlets. Electricity usage is not much at all. I put my pump in an insulated box, run the tubes to Styrofoam island moored within boat hook reach. Cold weather, snow; the rig handles it all, never lost a fish in western PA.

The best is none. Deicers have been a fav on web sites for the past few years but most ponds were fine without them for thousands of years before that and I suspect they'll be fine for thousands of years after the web and humans are gone.

Gas exchange can be a problem, but so can cooling your water. An iced over in ground pond will have water at the bottom of 39F because that's the heaviest water. Water colder than 39F rises (warmer water doesn't always rise). But if you do anything to disturb this natural wonder the water will mix and all the water in the pond can be lower than 39F...even going below 32F (unlikely, but possible).

Fish can survive in super cold water...for some period. Fish can survive in water with poor gas exchange...for some period. The question is which is the bigger risk for you? I've seen ponders in Sweden and Finland have gas exchange problems because their ponds ice over and stay iced over for really long periods. But even many of them don't use deicers. Instead they make sure the pond is clean before ice over. Rotting organic material causes the real gas exchange issue. O2 and CO2 are not the issue.

Most ponds in the US for example ice over for short periods of time, maybe a month at a time before a warm spell melts everything. I kept ponds for years in upstate NY and we had periods where it didn't get above zero F for a few weeks. But then it's warm up and melted everything.

IMO lower water temp is normally the bigger threat. Gas exchange is a threat but way over hyped online. I come to this conclusion just by looking at the millions of ponds in the world which ice over and the fish live. On the other hand dropping the water temp to 33-38F just can't be a good thing for fish. Most do survive deicers but lots don't. I've read cases of deicers breaking and electrocuting fish or catching fire and putting toxic chemicals into the water. And then many cases of fish dying but the owner saying it was because they didn't have a big enough deicer...and never ever taking a single water temp reading. My personal fav is when they say they had a bad cold spell and the deicer couldn't keep up and the pond froze over for a few days which killed all the fish. Every other pond on the planet can freeze over for months and be OK but not this pond. The concept of -30F air being pumped through the pond water driving the water temp down to maybe below 32F...no, that could be what killed the fish.

Scaring people is more entertaining and many people do like to buy stuff (even while complaining the whole way) for their pond and "fixing" nature because they want to feel smarter or something. Just depends on what aspects of the hobby you enjoy.

I live in Ottawa where my pond ices over for about 4 months. When my Thermopond heater died, I lost all of my fish. It uses 100 Watts and is good for up to a 2000 gallon pond. You could use 3 of them and keep your fish alive with no problem. Look them up on amazon. http://www.amazon.com/s/ref=nb_sb_ss_c_010/190-4798013-8949267?url=search-alias%3Dlawngarden&field-keywords=thermopond+deicer+3.0&sprefix=thermopond%2Caps%2C351

Perfect example. Thanks

Waterbug guy - I don't think I quite understand what you are saying. Are you saying that when it is -20 to - 40 celsius for 6 months during a normal northern winter my pond will never freeze to the bottom and kill my fish even though it is only 18" inches deep. or is it only if I have a perfectly clean sterile that doesn't have anything to break down and pollute the pond and no live creatures that might move and circulate water. I ask because I have had my pond freeze to the bottom the year my heater died and when the icecube finally melted off the bottom a number of my fish were frozen into the ice so I am wondering about how this happened according to this, or is there qualifiers you omitted like depths and duration and frost depths and temperatures.

My 1100 gallon pond is 3' deep except for the ledges for marginal plants and I can keep my fish alive using a single thermopond heater to keep a hole in the ice. An 18" deep pond will freeze to the bottom most winters in my area no matter how clean it is. Goldfish die if they freeze.

squirelette, heating and deicing are two different things.

What I'm saying is what I said. I would say a climate that never gets above -20C for 6 months is extreme north or polar. Like Sweden and Finland. I do assume people are bright enough to know an 18", or 12", or 6" pond in that kind of climate is probably not that smart an idea. 24" deep ponds are very common, without heaters or deicers, in places like MN which are pretty cold for long periods.

To list all the qualifiers would take a few books.

I didn't say the pond had to be "perfectly clean sterile"...that's you just being a troll. Thanks for reminding me why I don't like forums.

Thanks for making me feel like a fool now I remember why I dont like these forums Judgemental people who are so smart they dont have time to help others. And no you probably would not build my pond or pay to heat it I would not behave like you for all the tea in China either

My apologies. Perhaps you weren't trolling. Communication is difficult in forums and there are so many trolls. Your post sounded like trolling because the "questions" had an obvious answer. When a pond freezes to the bottom fish do indeed die. That's standard troll red herring. Also, exaggerating what I said into "perfectly clean sterile" which is an impossible state is how trolls try to put absurd words into another person's mouth in an attempt to make them look bad or at least start a flame war.

So I'm sorry if it wasn't your intent to troll, but that's how it appeared to me.