Deep Blue 34g RR back glass tempered?

[Hippo]

I have a Deep Blue 34g RR rimless frag tank and I’d like to drill a return on the back glass opposite corner of the drain. I came across this..

It says non-tempered, but the bottom is.
How can this be. The bottom corner is drilled with a 1” drain and 3/4” return. I’d like to use the 3/4” as a main drain and the 1” as a back up.

 

[Peace River]

IMO the best way is to test with polarized lenses and an electronic device (see youtube for specifics). I try to always do this before I drill a tank (test all panels that you are considering drilling). I have even found some that were tempered that "shouldn't" have been and found one that was clearly marked as tempered that wasn't and I was able to successfully drill it without an issue. Good luck!

 

[Hippo]

Not tempered.