If you enjoy making things, or just playing with soil and mud, use the mineralized topsoil for a bottom layer and add an inch of something that you like the looks of for the top layer. I tried Flourite black sand in a 10 gallon tank and really liked the appearance, plus the ease of planting in it. It would probably take two bags of it to top the mineralized topsoil. Another possibility, if you don't like playing with mud, is to contact torpedobarb (
http://www.plantedtank.net/forums/su...rate-kits.html) to see if you can buy one of his mineralized topsoil kits. Other than that it seems to be a consensus that ADA Aquasoil Amazona I is the best commercial substrate.