Thusly "Ionizer" Spake Unto All:


This afternoon, just half an hour ago, I came home to find another otto
cat jammed into the intake slots of our filter tube, hanging
motionlessly. Over the months, this is where I've found most of our
small handful of fish losses- I assume that they drift lifelessly and
end up being pulled gradualy towards the tube.

That's guaranteed to be the case. Otos are outstanding swimmers and
capable of navigating *any* current you can throw at them - he was not
sucked in the filter by mistake, he was almost certainly already
dying, and no longer able to navigate.
Once a loricariid (such as an oto) finds himself in danger, for
instance being sick and sucked against a filter, they react by raising
their barbed & spiny fins and locking them in upright position. The
reaction is really intended to make it hard for bigger fish to swallow
them, but in this case it may have got him really stuck.

As to why your oto was apparently dying... they're very sensitive
fish, and they also tend to have difficulties finding enough food,
even in aquaria with lots of algae. Starvation is probably the #1
killer of otos, at least those who manage to acclimatise and survive
the first month in a new aquarium.

However, that you've had more fish die suggests there may be some
other, more fundamental, problem than the inherent sensitivity of
otos.