"Sacha" wrote...
"Bob Hobden" said:
Don't forget water too, most of it out there is frozen solid and the
birds need to find some to drink. They use the filter outfall into our
pond which always stays unfrozen.

Bob, we stop the pumps running in winter on the grounds that it makes the
water colder if it's being recirculated. I think that's the reason
anyway! Presumably you don't go along with this theory?

It may do but the pump produces some heat to compensate and it's never a
good idea turning off a biological filter, especially a large one. All the
bacteria will die or be replaced with anaerobic types so when you turn the
filter back on you next spring you will effectively push the muck/toxins
back into your pond, bad idea.
The only recourse if turning it off is to strip the filter down and clean it
thoroughly leaving it dry and start again from scratch in the spring but
then it will take months to build up its bacteria to full strength. That
said you can purchase biological starters for them in bottles.

--
Regards
Bob Hobden
W.of London. UK