Nope, had gravois glass do it. You probably did not level the tank or you overtightened the bulkhead. Not leveling the tank being the one, I believe... A hole in glass is going to become the weak spot...
You will need to replace that botton glass or somehow patch it with another piece of glass covering the crack 6" in every direction. I would replace the glass anything else is just asking for trouble. Siliconing it might hold for now but 2 weeks down the road it will leak...