Originally Posted by 90galWavefront
Any decent size tank I ever had always had a tempered glass for the bottom. I personally would not trust regular plate glass for a tank bottom.
I wouldn't advise toughened glass. It has a tendency to shatter especially when struck on the corner (that's how we used to break sheets down) and also along or close to the edges.
There is also an occurrence of glass sheets just giving out for no apparent reason, I have witnessed this on several occasions. The glass is in part designed to break into small pieces to meet health and safety requirements in public areas and areas of high traffic. My personal preference for base panels is a laminated sheet. 6.4mm or 12.8mm will be suitable for most domestic aquariums.
A suitable thickness float or polished plate glass will be more than sufficient in almost every application. Where plate glass is not suitable you will be getting on for pond sized to public aquarium sized installations.
Suitable protection should be used for the base panel.
The alternative is acrylic, it's lighter and tougher. I have no experience with acrylic aquariums.