[Chin_Lee]

Kevin
Will you or do you have the means to remove everything from your tank to fix it in the future if it does start leaking? I think thats a critical back up plan that needs to be in place before you make the decision.

Having said that, I think its salvagable without removing the entire piece. My only big concern with the crack is that its at the bottom which means if the crack spreads, it will spread from the bottom meaning any leaks will drain the entire tank over time.

My understanding of the tank structure is that it has a eurobracing at the top and the bottom - is that correct?
If thats the case, its the same tank manufacturer as mine and I have to say the tank is quite strong structurally. The way I see it, the crack will spread if there is any bowing in the glass. I would put 1/2" piece of glass that is as wide and big as possible and sandwich the cracked piece and the inside of the overflow entirely - kinda like overkilling on eurobracing the inside of the overflow as well as the outside part.
Another consideration is make sure your stand and tank is completely and immaculately level. Deviations in the levelling will increase stress point on your tank and in your case with a 84" long tank, this may cause the crack to spread.
If it helps, I can put a straight edge onto my tank to see if there is any bow at all ; my tank is a 300g cube thats 30" high. Unfortunately its only 1/2 the length of your and slight bowing may be even be present with such a your long tank. I will look into it tonight when the lights comes on.