Carole, I'm certainly not a pond expert but I'll share what my husband and I have learned by trial and error. I am sorry for your fish loss. It's awful to lose a fish, esp. a favorite, no matter what the circumstances (ours were due to herons until we wised up). I didn't read every post word for word, but it sounds to me like it could be due to oxygen depravation. We've had our pond for a few winters now and our winter treatment is very simple and it's served us well. Once we do the fall cleanup and turn off the waterfall, we insert the bubbler until we do the spring cleaning and turn the waterfall back on again. The bubbler is on the bottom of the pond, but shoots water high enough to keep the surface water moving. Some folks have told us they don't use bubblers and their fish survive just fine - however, I think that's pretty risky up here and I won't try it. The moving water helps delay the freezing over. Usually late January is when I have to put in the de-icer and it's only in until early March. This year was pretty brutal coldwise for us in the northeast. We use the donut shaped Thermo Pond de-icer. Our pond is 2,500-3,000 gallons and it's been sufficient. Over the years, we've lost a goldfish and two black moors, but never a koi. Nothing died this year. The only problem with the de-icer was this year when we got an extremely heavy snow during a bad blizzard. I had to keep going out and pushing the drifts off the de-icer to allow the surface to be clear. I hope you figure out your problem. I have noticed that sometimes we tend to overthink our ponds, when the solutions are usually pretty simple. People are very knowledgeable on these forums, but you're pulled in too many different directions when the answer isn't that complicated. Best of luck to you.

Waterbug guy, First I will talk a little bit about concrete in water. You say it is a myth that concrete in water can kill fish and raise the PH. When concrete first sets up the surface PH is 12.0. Which is the same PH as a drain cleaner called "draino". As it is exposed to the CO2 in the air the PH goes down. But water is a very good leaching agent and so water will continue to try and get the chemicals out of the concrete. So will the PH in the water be raised? If the water has normal PH of 6.5 to 8.5 the answer is yes. The real question should be "how much will it raise it"? That question isn't easily answered as there are a lot of variables. Just to list some the age of the concrete, the condition of the concrete, is the water flowing over the concrete, the natural PH of the water, is the water being changed, and the volume of the water versus the contact area of the concrete. In some cases the rise might be so low as to make it very difficult to measure. But in other cases it can and does raise the PH to 9 to 9.5. At these levels it can and does kill fish. If I remember correctly you have stated that you are a pond contractor. If you are I hope you having started using roofing liner in the ponds that you build. Most of the time a person on this forum is never going to have a problem with roofing liner. Can there be a problem with roofing liner? This should be the question. The answer is yes. The chances that there could be a problem is very low. The largest pond product manufacturer in the US sent out a letter to all their customers a number of years ago. This letter said that all their liner in the future would be tested to be fish safe as they got a batch in that was not. In other words they were selling roofing liner as pond liner. This company had been selling a lot of liner for 10 years before this problem. If it had happen today with the wide use of the internet I would have think that some lawyer would have gotten this information and started a class action lawsuit against them and they would be out of business. The lawyer could easily have sued them not only for the cost of the liner that they had sold but for the cost to replace all those liners in the ponds built with them going back to the first time they sold this liner. The largest liner manufacturer in this country has told me that almost never would you ever have a problem with roofing liner but you might. I think that as a contractor you can't take that chance. If you were unlucky and did have a problem and were sued over that problem the lawyer handling the case would find out that they would sue for every customer that you have that has this liner. In other words you would be out of business. So is roofing liner toxic? No most of the time. But there is a small chance that there maybe a problem. I have only talked about 2 of the 8 things that you listed. I could easily talk about many of the other things listed but my point is this. You listed these things as black and white but they are not black and white. The only thing that is black and white about ponds is that all aquatic life will die. Mike

My 2 cents worth. We have occ. prolonged periods of below zero temps, mostly less than a week, but below 20F for up to 3 weeks at a time. 2 years ago I dropped my plants to the bottom, left my eight 4" goldfish/comets in and had a 100w de-icer with a tiny airstone about 18" under it. My pond is 5'x5'x28", 300ga. Everything survive and flourished, except a couple tropical type plants. Last winter, I did the same thing, but when we had a long stretch of sub-zero temps, my de-icer froze over for almost 3 weeks. When the temps got above 15F it opened up again. But I lost all my fish, several hardy water lilies and all of my pickeral rush. We had no snow cover to help insulate the pond. It didn't freeze to the bottom, but I think the toxic build up killed the fish. THIS winter, I'm going to use a 1000w stock tank heater, and put a sheet of insulation or plywood over most of the pond, as well as use my little air stone. Yes, tank heaters only run when the temps are below their thermostat setting. So while they do cost money to run, not as much as most people think IMO. I run 2 or 3 for the sheep all winter, and my electric bill isn't that high. Certainly not as much as replacing plants and fish. An added note - no matter which way you go, please be careful if you have children or pets if you have open water or thin ice. The birdies love it, but you don't want a serious accident! Again, just my 2 cents!

Toofast, I'm over to the other side of London,Ontario, so not so far from you and our winters are much the same. I don't run the main pumps over winter, I'm wary of ice dams being created and water being diverted away from the pond. I shut the waterfall and statuary pumps off for the winter, but, because of where my bottom drain sump is located,I run a small 500 GPH pump all winter to circulate the pond water and create a vent opening in the ice. The 500 GPH pump is located in the 50 gallon bottom drain sump, and pumps water through a 1/2" hose to the pond, where it keeps the surface water moving and allows for gas exchange. I have a 1200 watt deicer as a stand by in case of pump failure. I also totally cover my ponds over, first with a leaf net for a month or so, then with a translucent tarpaulin supported on a frame, for the winter months. That keeps the cold winds from blowing across the water surface. Your plan to use an aerator and a small deicer, with your large wattage deicer as a stand-by sounds great to me. As far as keeping your pump in a bucket of water, there is no need to do that, as mag pumps,unlike oil filled pumps do not have seals that will crack, if they are allowed to dry up over winter. But that is up to you. March would be a tad too early for start up,I should think. I push the envelope a bit by getting going at the beginning of April. And that is dependent on weather conditions. The main clean out the pond, I do in the Fall, rather than in the Spring. That way I'm not stirring up the "nasties" from the bottom of the pond, when the fish are still very susceptible to disease after going through a hard winter. You mention a check valve "sticking out of the water". As long as it is not filled with water, that could freeze and cause the valve to split open, it should be okay. If you could remove it and take it apart for cleaning and then store it, that would be a safer solution. Check valves should be cleaned out at least once a year, as the are a real collector of gunk and that can cause them to stick open or closed. The same goes for your pump. Take the impeller cover off and clean it out before storing for winter, whether it is kept in water or not. The gunk inside the pump can [and will] set up like cement over winter and cause the pump to overheat and possibly burn out when you try to use it next Spring. Hope this helps. "Horton"