OK, but I'm still concerned. Any "modern" tank of 4 or 5 ft has a center brace...how thick is the glass? "Original" glass brace?? What are the dimensions of this tank? I had a "DIY" 40g long rimless that had very thick glass & a glass strip in the bottom to "support" the sides, no bowing at all, but your tank is much, much bigger...I'm worried it's a reptile tank, silicone & glass isn't "original" equipment on any tank I've seen, "under the rim" less so. Silicone is stretchy, not supportive against water pressure...
I dont understand your concern, its had a center brace from day one. The glass that makes up the tank is 3/8" thick. The tank is 60"L x 18"W x 23"T. This wasnt a reptile tank, it had an overflow box when i got it for a sump filter, so it wasnt a reptile tank.