what glass thickness shoult i have it will 4' long 2' wide 5' tall it will onlt have about 4" of water in one half of the bottom. it wil have a single aussie water dragon
the structural load is minimal and there is basically no water pressure so you could go pretty thin. your biggest concern should than be damage from an outside source. its basically a window. 1/4" should be lots imo unless you like playing football in th house