"Koi-Lo" Reply to NG Only wrote in
:

I would think the bacteria would start to die that many hours without
a fresh flow of oxygen rich water. I personally wouldn't do that.

The bacteria certainly wouldn't die. Nitrosomonas and nitrobacter bacteria
are a lot more resilient than people give credit.

What would happen is that the lack of circulation would prevent the
bacteria from doing its job properly. The low levels of dissolved O2
combined with the high concentration of ammonia present by morning would
mean it would take time for it to be processed out of the system once the
filter is switched back on.

The pH would being to climb the moment circulation resumes as all the
built-up CO2 is forced out of the system, making the lingering ammonia all
the more dangerous.