Hi,
My daughter has a Bi-Orb in her bedroom in which she keeps 2 goldfish. How does this relate to your question, well I would refrain from using one as a nano venture for a couple of reasons, firstly its acrylic and round, rockwork will scratch it severly, secondly they are an absolute nightmare to get at to clean. try getting a decent sized net in the neck opening. pretty labour intensive to maintain.
Dont let me put you of,f just making you aware of the negitives I've come across.
Regards
BigC