This link describes a tank set-up with a substrate that I wouldn't recommend. The soil is too thick (1.5 to 2 inches), and it consists of a clay/peat mix that will generate lots of iron and algae problems.
However, owner (DLevy) was able to work through the problems and eventually get a very nice result.
http://www.aquaticplantcentral.com/f...-new-rain.html