Marie; I also live in zone 5 and this is what I do; last year I put in a pond breather (go to the Winterizing forum and look for threads about the pond breather, if you're interested) and also augment that with an aerator suspended about a foot below the surface (I've read NOT to place it at/near the bottom). And just for emergencies, I bought a cattle trough heater to melt a hole if I need to. The idea is to try and keep a hole open in the ice so any toxic gases that might build up are released. The aerator isn't to provide oxygen, it's just one way to keep a hole open. Since Michigan had such hard winters the past two years, I found I needed the pond breather too when the ice pinched/cracked my airline. Depending on fish load, organic decomposition load and surface area, having the pond covered by ice isn't necessarily a bad thing. Once the water temp hits 39 deg F, the water will invert and the coldest water then is at the surface, not at the bottom where your fish will hang out. I've also read that it's a good idea to clear the snow away so sunlight can penetrate the ice. Re your pump; mine is a submersible and I unplug it as the ice begins forming and leave it in the pond near the bottom. It'll be fine stored that way.