After shoveling out 250lbs of gravel, I was able to pull the aquarium away from the wall for a closer look. Sure enough, the cracks were bad:
I couldn't understand what would have caused such a failure. I hoped that it was a manufacturing defect. I pried off the plastic trim along the top hoping to find a chipped edge or an unclean break, as that would be my evidence to complain to Oceanic. Unfortunately, as you can see, it's a perfectly clean edge. A single crack leaves the top edge and splits out to multiple cracks.
I had three theories for the failure. (1) Manufacturing defect. (2) Overheating of the glass by the heater when the water level in the overflow box dropped and I hadn't remembered to turn off the heater. (3) Uneven support by the stand.
I did have some instances where the 500 watt heating element was not fully submerged and was on. But it sat on the bottom and the crack started at the top. I had some concerns about the stand design, but I reasoned that if it wasn't fully supported across the span, it should have created inward pressure at the failure point. It seemed like it would have had to be supported in the middle and not the ends, thus pulling at that point, in order to crack at the top. Neither seemed to have occurred. Once I saw where the crack was and found no apparent manufacturing flaw, a fourth option came to mind. I had drilled several holes in the wood supporting the bog in order to create a large notch along the front edge. The plan was to use the notch to route hoses and wires into the tank, but it ended up not working out. While drilling, I think the bit may have broken through the wood and allowed the bit to hit the edge of the tank. If it did happen, it left no apparent damage on the trim, and if it caused a flaw in the glass, it didn't manifest itself for over two months of water testing and startup. So I don't know.
The warranty on the tank said it covered only "glass-to-glass seals" and "only if the tank is used on an Oceanic stand." The crack therefore didn't qualify, which seems unfair. But such is life. I started to consider replacement options. I had a good relationship with my local fish store, so hoped they would let me order a replacement at-cost. When I stopped in to inquire, I discovered that they had had a fire in the store a few days earlier. While they were loading most of their stock onto a truck to take it to their other store in Houston, they were looking to sell some of their display tanks. None fit what I was looking for though, so I passed.
We ended up ordering a tank from GlassCages.com. Since we were reconsidering things, and I was going to build a new stand, we picked a 240g 72x30x24. The 215g was 72x24x29 which made it too tall to comfortably work in. This would give us more depth to the tank for visuals and it wouldn't be as tall so it's easier to work in. GlassCages builds their tanks on demand, so they would build to spec. I opted to have the holes drilled in the back glass rather than the bottom as I felt it would make access easier. I also liked how a friend who recently opened a fish store did his tanks with home made skimmers. (More on that later.) I opted for a 5th hole to be used as a dedicated drain for water changes. I thought the tank would have cross bracing as the previous tank had, but because GlassCages uses euro-bracing, this tank didn't require cross bracing. This was exciting as it made the top almost fully open. We also upgraded the front glass to StarFire glass which is low in iron content and lacks the blueish tint most thick glass has. GlassCages is in Tennessee, and for only $80 would meet in the Dallas area and transfer the tank to your truck.
It turned out that by Dallas, they really meant Denton which is almost an hour North. So after a long day with a rental van, much sweat and frustrations, we got it home. Here it is.The euro-bracing is the rim of glass around the top and there is one at the bottom inside the tank too.