"Rusty Hinge" wrote ...
Bob Hobden wrote:
"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.

If it's a sand filter the organisms within are algae, and will be quite OK
so long as they are kept wet.

Even if they do die, a fortnight's running will 'seed' it with freh algae.

Sand filters are not usually biological filters, or I should say biological
filters don't use sand as a growing medium for the bacteria. Sand filters
are usually pressure filters for polishing the water.
Lava rock, bits of cut crinkly pipe, filter foam etc are used in biological
filters so there is little effect on flow rates and they have a large
surface area for the bacteria to grow on.
Dead bacteria and the resultant toxins are not what you want being pushed
into your pond in the spring when the fish are getting over a long winter.
Water quality is everything where fish keep is concerned and a build up of
Nitrites etc is bad news for fish health. Clear water has nothing to do with
the quality of the water in this respect.
Running a clean filter will gradually build up a bacteria base but it will
take some time to get to it's optimum working density which is why a lot of
people use a "starter" solution to seed the filter with the "right" bacteria
so it has a good start and to try to avoid toxin build-up as feeding
commences.

--
Regards
Bob Hobden
W.of London. UK