In my research with builds that I did before I did mine, I learned that you need to either do the aliflor layer on the bottom for filtration/drainage/humidity or a false bottom made of a material called egg crate which is a plastic grid of squares. I chose the aliflor layer because its hard to disguise the egg crate. You put a layer of that, then a couple of sheets of screen or landscape cloth, then you put your planting media on top. That is what you actually plant the plants in. I use a mix I have used for plants in the greenhouse for years. This photo is a small example of the depth you need. My 75 gallon (shown here) has a depth from the bottom of the glass floor to the top surface layer of the planting media of about 6-7 inches total. In my 20 gallon its about 3 inches. The 75 gallon is deeper because I needed a water reservoir under the planting medium to run water pumps for a water feature. You would not need it so deep. The 20 gal does not have a water feature so that sort of water reservoir was unnecessary
