I don't have experience with a tank of that size... But you will see a significant bow in almost any long tank. (maybe one of the reasons they're not that common)
I doubt that it's going to break, but all materials have some flex. And at a length to width ratio of 3:1+, I would expect it with non-reinforced glass. If you want to think like an engineer, find out what the modulus of rupture is for that particular grade of glass, and calculate the breaking strength. Or, just ask them for a data sheet. Whatever you decide to do, trust the data - even if your intuition wants you to believe otherwise.
Personally, I would have gone with a Euro brace. I just don't like bend-y glass, when I'm trying to fit things like lids. (which isn't your situation, but just relating my own experience)
I doubt that it's going to break, but all materials have some flex. And at a length to width ratio of 3:1+, I would expect it with non-reinforced glass. If you want to think like an engineer, find out what the modulus of rupture is for that particular grade of glass, and calculate the breaking strength. Or, just ask them for a data sheet. Whatever you decide to do, trust the data - even if your intuition wants you to believe otherwise.
Personally, I would have gone with a Euro brace. I just don't like bend-y glass, when I'm trying to fit things like lids. (which isn't your situation, but just relating my own experience)