To the folks who drilled your tanks: How did you definitively
identify that your tank was tempered glass?
Mine is a 60 gallon. I have been looking all over the internet for tips. Found a ton of information but when I check myself, it does not pan out. So far...
1. The polarized sunglasses test
This trick does not seem to be definitive. I have tempered glass on many window panes in my house, the polarized sunglasses test does not indicate that the glass is tempered even though those panes have clearly markings saying tempered glass. It did however show the vertical lines on the side windows on only one of my 2 cars. I suspect those lines come from laminated glass, not tempered glass, although the articles say those lines come from glass sitting on rollers during manufacturing.
2. Edge smoothness test
The edges of my tank panes seem smooth, like the photo below (photo credit in PS#1 below). I'll see if I can get a good photo of my tank's panes.
By the way, I have a old 10 gallon, its edges have tiny serrations/imperfections from when the glass was scored. The 60 gallon does not seem to have them. Again, is this a good test? I do not know.
I want to drill my tank for an overflow and return. But do not want to find out the hard way
if it is tempered or not.
Here are some photos of my tank's glass:
The swirls in the last photo are coming from a reflection from an IKEA paper light standing next to the tank.
PS: I have read many articles, some of them are here: