[Surfhead]

don't let the top freeze solid again. make sure you keep a hole in the ice. an air store or floating heater will work. use a pick axe if you have to, just keep a hole in the ice. the brown water is probably run off from the rain. too cold for a bacterial bloom.

when you say "mid-size" how many gallons are we talking here? what % of the pond is 3 feet deep?

no more food, maybe add some koi clay to help with the toxins. I hope you used dechlor when you refilled.

Is there any chance the pump will freeze? If so then you need to turn it off and rely on an air stone. If the pump freezes up, you might as well throw it away.