as mentioned somewhere else
for those concerned about curved tanks and the tendency to break, the nano are not that at fault. Its more the bigger tanks, 3foot and up that is prone to breakage. And not all the makes either. It depends on the process used and how long they took to bend the glass. Too quick, and the glass stretch and is in fact thinner at the corners.
In my opinion, another problem with these cubes are the closed lids. They cause the tank to run at higher temperatures than is acceptable and they limit the light options. A lot of guys do change it. These tanks are not really designed for our sunny South Africa.
The tanks tend to crack on the corner, sometimes not even running all the way to the top or bottom. What can you do to prevent it. First ensure that the tank is level. And that the wooden base is not swollen over time and warping.
Also do not put the tank in a draft. Where cold or hot air blow past. Especially where the temperature can quickly change due to you opening up some doors to allow wind to blow through.
(About 2 years ago one guy on MASA had a tank that cracked. And it was empty, in Natal Midlands somewhere in winter time. Can not remember who)