Have you prepped the pond for winter yet Marshall i'e removed any detritus dead leaves etc fro the ponds bottom cleaned the filter etc , the more you can do readying it for winter the greater the chance of them coming through the other side my friend .
I have three large vortex style filters that I ready cleaning them the fourth a barrel filter full of K1 I leave running 365 days a year .
The other three are cleaned well two get done every 3 months or so as part of an ongoing maintenance program .
The first filter has no media of any sort and it cleaned weekly in the summer bi weekly during the winter .
I also do a partial water change even during the winter months .
This is done by trickling the water slowly through our dechlorination filters allowing the colder water to be warmed by the ambient temperature of the water in the pond.
Being under policarbonate sheeting my water never freezes and even at -15c we can maintain a temperature of 7c
On warer days this goes up to around about 9c.
This October has been very warm indeed for the time of year and under the roofing sheets we still have a temperature of 15.2c with a night time air temperature 9c so as you can see this method does wor and work very well .
Dave