I am in Orlando so I do not have any experience with zone 6! We are in zone 10.

From what I know the bacteria that are in the filter, waterfall, biofall, or whatever system you have pretty much dies in the winter. I understand that you have to have a hole open in the ice to let the gasses escape and oxygen in.

If all else fails move to Orlando and I can build you a swimming pool.

Hope I helped a little... I know nobody else is posting in here.

Jason

I have always kept my filter and waterfalls running for 15 years of ponding. It keeps the water oxygenated and except for the very cold winters, keeps at least a small area open. I keep the filters in as well and they gather quite a lot, even though the water is cold. I have lived in zones 4, 5, and six.