You really need the drainage layer for the excess water to drain into. This keeps the substrate from becoming water logged. That will hasten the breakdown of the substrate but also could lead to a smelly tank.

SO you need.


Surface Material ( Something like ABG Mix)
Substrate ( Coco Fiber)
Mesh/Filter Material ( This keeps the substrate out of the drainage layer)
Drainage layer ( Expanded clay balls, large gravel, egg crate)