By looking at the picture of the broken tank I would say it was definitely a failure of the center brace. A 6-foot tank will bow out noticeably and a well constructed center brace is of the utmost importance. It is difficult to tell what size glass you used for the brace, but it appears to be a bit thin in the picture. Look at Oceanic (brand name) glass braces for a comparison. Silicon gets stronger after a few days and filling a tank prematurely can weaken the adhesion. Failure to properly clean the glass prior to applying the silicon can also result in a weaker bond.
As you have probably learned by now making and repairing aquariums is probably best left to the experts. Filling up home repaired tanks outside is defintely a wise idea. The shorter your aquarium the better your odds of success, as pressure increases with height.
As you have probably learned by now making and repairing aquariums is probably best left to the experts. Filling up home repaired tanks outside is defintely a wise idea. The shorter your aquarium the better your odds of success, as pressure increases with height.