Taking a page from marine fishkeeping...
Is it practical to construct a (decorative) sump where you can
hydroponically grow houseplants that also act as a biological filter?
From experience lots of arums (philodendron, syngonium) do very well
grown hydroponically. And since the plants breathe atmospheric air, no
trouble from in-tank plants depleting oxygen at night.
Problem is, I don't know any plumbing. No chance building a sump this way.

Seb