The nano aquarium can sometimes be a tough nut to crack. On the one hand, they are low-volume systems that are typically easy to maintain. On the other, they are not as stable because the water volume is minimal and the equipment is usually lacking, for one reason or another. To avoid the major pitfalls of the nano tank, we think understocking is the best approach. Too often, we see nano aquaria filled to the rim with large fish and loads of corals. While the corals don’t bother us, assuming they are doing well, it’s the site of clownfish and other moderately sized fish in these tiny aquariums that really irk us. Nanos have almost zero swimming room, and therefore limit themselves to fish like gobies that don’t swim much at all.