Sam,

It's in a way funny to read how much there can be "cultural" differences on
this matter... let me explain: at least with Koi ponds, most Dutch/Belgian
people would advise you to never turn off your filter in winter, and some of
the reasons for this are valid for "ornamental" or "other fish" ponds as
well IMHO. (I think The Netherlands/Belgium are in "zone 7 BTW" )

Even though the bacteria will go in a dormant state at the temps you
mention, they at least do survive. Shutting off the pumps/aeration will
kill them off, and in spring you start all over again with a biologically
dead filter. (or worse, the dead bacteria actually turn into a toxic mulm
if you don't meticulously clean the filter/pipes before startup again)

So the "consensus" for the Dutch is to keep the biofiltration running,
albeit with a reduced flow. This way the biofilter will start up faster
and without funny nitrite spikes you often see with a new filter/biofilm.

Mind you, I'm not saying it's the absolute truth, but quite a lot of people
with 10 years plus experience in koi keeping would not even dream of turning
off their filters.

It does bring along other problems of course, so often these ponders will
cover their pond and often use heating to keep the temps "consistent".

Of course this all depends on things like budget, overstocking, price of
their fish etc, one may not want to do this "overkill" on say 2 goldfish
(although, you want them happy anyway...). They also have considerations
like being able to feed throughout the year (higher growth), avoiding the
10 - 15 °C "aeromonas alley" etc, so it's important to emphasize that a big
koi pond is of course not the same as a small ornamental pond.

Still (I'll keep it short LOL), I think it's fair to say that you destroy
your carefully built-up biofilm by shutting everthing down, and people with
lots of algae problems or dying fish in spring might want to take this
"different" approach into consideration. We all know about the "1st year"
syndrome, and perhaps the reason why it's not so bad the second year is that
the bacteria *in* the pond at least survive somewhat.

Thought it was interesting to mention this amidst all these "winterizing"
threads

Theo


"Sam Hopkins" schreef in bericht
.. .
The bacteria will continue to do their job until the water temp reaches 39
degrees. They will pause between 32 and 39. So if your temp is going from
say 35 to 50 I'd leave it on. If it starts staying under 39 you can turn
it
off.