Wow, impressive video / job weighting down that tank!
Hmm, I haven't used anything in the bottoms either. Wondering with my new tank, the low iron glass scratches more easily and is more brittle.
I broke my other low iron tank bottom a few years ago when it slid out of my hand during cleaning it out and I raised up my leg/knee to stop the fall and the knee impact popped it (smaller 12G tank and much thinner). It wasn't tempered glass.
So dropping a rock / rock slipping off its spot, could cause a problem.
In the middle of setting up both tanks. The other is a Waterbox 2418
The bottom looks just like the glass of the sides - being low iron. Glass thickness is 12mm /.472 inches.