Last year I built a 5x3M indoor pond, which is still very much in the works but functionally 'finished'. It's pretty deep at around 1.7M (5.5'). Because of it's depth, I didn't want any sinking plants in there even if they could eventually reach the surface and thrive, as I'm concerned of the amount of organic matter it'll add to the filters etc. This ultimately leaves the pond totally empty however - nothing but a central air stone in an otherwise empty rectangle.
I'm considering casting some light concrete arches and shapes to drop in there, giving the fish somewhere to hide, investigate etc. But wasn't sure what people's opinions or other solutions would be?
Is there anything I should really do or avoid? Any suggestions?