Nano tanks are eligible for TOTQ. They are one of the main reasons for the 6+ month requirement for TOTQ. It's easy to go out on day one, fill a nano with coral, and have a beautiful tank, it's much harder to keep it looking like that long term (and 6 months isn't even long term). In my opinion beginner tanks should not be eligible for TOTQ because they have generally not been established long enough and part of the allure of winning TOTQ is showing off how hard you have worked over a long period of time. Part of the purpose of TOTQ is also the write up where the winner can impart their reefing knowledge which will be the basis of how their tank has been so successful for so long. Beginners should always post a build thread and show off their tanks though!