Bioactive setup relies on the plants for uptake (e.g. nitrogen and phosphorus) from the soil. Then a Cleanup Crew of isopods and springtails live in the soil to break down decomposed matter into soil nutrients. Naturally occurring beneficial bacteria help the process in a balanced setup. It takes a while for bacteria to develop in the system so I used BioShot (from the Bio Dude) to start it off.
There is no need for a drainage layer as a ball python setup doesn’t produce much waste water. The soil absorbs waste as the CUCs feed on them. But, I did add a layer of hydroton to the bottom of my setup in case we over water plants.