I don't think Colleen had a choice but to clean her filters, and it was too cold to do them outside. If her filter is not kept cleaned out, the pump runs too slow, and ice forms more quickly.
I understand what you are saying about the water level in your top ponds staying constant, not going lower with loss of water, so I get that part, Colleen. Thanks for continuing to drill it into my head! My stream, which flows into the goldfish pond, has ice covering it, but water running below the ice. I shut off the heaters on both ponds, temps here got down to 9 this morning, and going lower in a day to single digits for two more nights in a row, then warmer, then colder again. Sooo tired of this see saw crap! I turned on the heater in the koi pond, but now the aerator hose is froze, I guess. But, I'm not concerned, temps going up to 40's on Sat. so it should thaw out. I want to see if the heater will melt a hole, then going to unplug it in the morning, or maybe tonight yet! Just wanted to see how long it took to melt a hole. I have a floating heater, is that what you use, Colleen? Remind me, too, is your heater in the bottom pond, where the pump pushes water to the top pond? And, how do you keep the water lines free of ice if they are outside of the ponds where the water circulates from bottom pond to top ponds? I know how you have your overflow from pond to pond, but I think you have water lines outside the ponds. My line that I buried only about 12" and that is above ground level, froze so I couldn't get the waterfall running last weekend, and it was so nice and warm, too. Ho hum .... Just going to have to be patient and wait for spring to arrive, I guess.