as i recall true water lilies (nymphaeacea) need 6 - 20 inches of water over the root crown depending on the type. dwarf lilies like nymphaea minuta can be grown in an aquarium, but they need more than 3 inches of water
Amazon frogbit looks like dwarf lily leaves, and grows large enough to support the weight of firebelly toads. (At least the small ones I've seen at the lfs, I poersume they don't get bigger...) Otherwise, you can likely find a plastic water lily or something similar online if not at your lfs.
Select from 12 to 18-inch basket of lilies in your plants. Fill the mix of land three quarters basket full and heavy, like earth. Light potting mix that you are using indoor plants for decorating floats away, when immersed in water. Remove the lilies in the pond basket, and all that, in late autumn, if they are in an area where the pond freezes in winter. Wrap in plastic and stored in a cool winter. When spring comes, pull the dead leaves, fertilize and put back in the pool.
I love my banana plant but I think more like it require for it, and I know it needs more than 3" . You might have to add some boulders or wood in place of the pads.
Water lilies are divided into two main categories: hardy and tropical. Hardy water lilies bloom only during the day, but tropical water lilies can bloom either day or night, and was the only group to contain blue flowers.