Yes but I have seen much much colder winters down here, we just lucked out this year and got lots of Chinooks. I remember the very cold winters very well, minis 45 for weeks at a time. My ponds only had little tiny openings, and I had only the one 1500 watt heater to keep all three ponds open, and the bottom ponds had so much ice on it I could walk over it. The trick is to leave a pump running beside the heater so the pond water is heated more evenly. Have pump out into the deeper part of pond on a crate or something, with the hose running to the heater, this will circulate the water and heat the pond better. It can be done, just not very well with a bubblers here as our temperatures are just too cold. We are very windy here too, similar to Lethbridge, and I lose lots of water to evaporation as well, as I have posted before. I top my ponds up every week, run a hose out the window. We both have had a mild winter compared to what we both have seen. Neither of us has had the real cold yet, coldest I have seen so far is only minus 25c so, have not had the minus 40c yet like we have had in the past, and like I said, been doing this for many many seasons and remember some years it snowed the first of October and the snow never left till spring, and months of plugging the heater in non stop.