Dan's nano build

[Snaz]

I think you can ID tempered glass with a pair of polarized sunglasses. Something about seeing a checkered pattern in the glass, the same effect seen on automobile windows.

[BlueAbyss]

Hey Dan, looks pretty good.

I would suggest drilling also, just remember that you don't necessarily need to drill the bottom of the tank since you are doing a peninsula style anyhow (you could easily drill one of the short sides). The sides are less likely to be tempered, and as Snaz suggested you can use polarized sunglasses (or polarizing film) to ID tempered glass.