Ooooooh! Very nice!
On the new tank I could imagine a field of green carpet up front with rocks used to make a mountain range in the background with a "dirt" (sand) pathway leading from the front of the tank going up to a split in the center of the mountain range. Of course tapering the pathway (as well as correctly sized plants) so the depth appears even greater. Just my envision though haha.
You should try out some sort of backgrounds, even on the first tank, maybe white, or sky blue even. Might make it look that much more majestic.