On sunday the base of my 4'x15"x15" tank cracked. I brought the tank second hand and had it set up for about a week. I had a lot of big rocks in the tank (was set up as a rift lake cichlid tank), and initially thought that was the reason for the break. Talking to Brian at the goldfish bowl today, he said it was more likely my stand may not have been level and that was more likely the cause of the crack. I'm having the tank repaired, and I'm wondering what thickness glass to use for the bace? I was thinking about going for 10mm (the rest of the tank is 6mm) as there will be a lot of rocks in the tank. If it was the stand that caused the crack then 10mm wont be necessary. Is 10mm over-kill, or would it be better to over-engineer??