I was thinking about it last night and I came up with something great.
Let's say the tank is 20 feet long, 12 feet long, and 5 feet high and let's also say that equals 10k gallons, it doesn't but let's just say it does for now.
So we put a big sheet of acrylic that measures 10 feet long and 12 feet wide on it then we cover it with dirt, plants, moss, and what not. Think of a jungle floor. Also some small jungle like trees.
Next we build a bird cage surrounding the perimeter of the top of the tank, all 20x12 of it. In the tank we'll have a variety of small fish, some minnows, tetras, and some larger fish that will eat some of them. Some snails, crayfish, and lots of plants and driftwood for hiding places. Make it have a nice sand bottom.
Now we get a bunch of small frogs, think dart frogs and such, and let them live on the 10x12 area above the tank. We'll put in some bugs and different things that'll breed and provide a food source.
Now just maybe we'll have a bird or two that'll also live in the cage. It can collect nuts and seeds from the small trees and eat some frogs, bugs, and fish. It'll be a whole ecosystem!