Yes, Bartian, – I understand your point about filtration, but to be honest – in the bigger tanks (60 ) of which I have 3 now with groups of paros (10-12) and where the two of them now is running with a small slow filter, the ones with the filter seem to feel better.
I only took the one out of this one because I needed it in another tank, and it seemed to also have lost a lot of power. But I will prefer this to an air pump, which makes too much noise for a living room tank.
And I think they like a small current.
Its really interesting what you both write about the labyrint organ.