I think a nano is something less than 10 gallon
But I think there is more to a nano than just tank size. I feel like there is s certain level of the KISS methodology associated with nanos. For example, on RC, there is a build thread for a 10 gallon with radions, mp10s, a GHS profilux, top off, and dosers. Does this really count as a nano?
34g or less. Bio-Cube makes a 29g.
How about going a poll style thread?