"Yowie" wrote in
:

Fair enough - although they haven't died when we've had power outages.

Luckily most fish are quite hardy, and I think that none of the species you
have there are high-oxygen species. Some river fish, like Siamese algae
eaters, might die (or jump out from the tank) quite soon after the oxygen
level starts going down.

The bacteria dies due to lack of oxygen?

Yup. Not all bacteria, but the ones living in a filter dealing with
nitrogen and fish waste live there just because they need quite high level
of oxygen.

It is most definately not vibration against the glass as I have
cushioned it all to no avail.

Okay, you have already checked it. Then my advice doesn't work.

Liisa