Bummer, but like I said, this is good experience no matter how you look at it. There are a lot of keepers here who are all talk, it's nice to see a new keeper who's not afraid to put in some effort. A few things to improve on if you try again:
-i don't think this tank cured properly. Immediate cause of the failure imo. Next time build in a sheltered area that won't get too hot and is out of the sun.
-Let your tank cure for at least a week, 2-3 weeks even better. Small jobs will be ok after 72 hours but the silicone deep in the seams takes a longer time to cure.
-make sure you leave no gaps in the silicone when you're laying in a bead.
-you will need to use some sort of mechanical braces to clamp the vertical seams of your build. Even if your bottom seal had held up I don't think the sides would've made it over half full. The duct tape was insufficient imo. While glass appears quite smooth, you need pressure on the seams to force silicone into the microscopic nooks and crannies of the glass and get the best hold. Just dont overclamp like I mentioned before either.
Best of luck if you try again someday. I know theres been criticism as far as the "value" of rebuilding a 55g, but make no mistake it's well worth it to make a first build attempt on a tank this size...you don't want to make these mistakes on a big tank that could really do some damage.
Matteus moving thread when he just couldn't get a break from bad news.
