240g of water at 8# per gallon equals 1920#, so yeah just shy of a ton not counting the glass so overenginerig it would be best, exspecially with small children around, also I would put some steel bracing on the corners. oh and a really cool thing to think about is a good ration of tank to hood ration is to make it a 6th of the tank height and it will look ballanced. Oh and in Ohio what quality is the lumber here good lumber is hard to find and freaking outragouse priced and the cheap stuff should be labelled in the store as "crap only good enough to burn".
just my two cents, nice build and good luck.