The Dude's all new HydroGrow V2 is the common standard for when it comes to terraria drainage. The Dude's Hydrogrow V2 MUST  be used with a screen divider. 100% natural clay, this drainage layer effectively captures excess water out of your bioactive substrate while effectively aerating top to bottom, preventing anaerobic water pockets. Boasting a natural color, the Dude's HydroGrow V2 is the go to for vivarium drainage.  It is recommended to rinse off HydroGrow V2 prior to using in your terrarium. 

HydroGrow is not needed for Terra Firma, Terra Sahara or Terra Aranea bioactive substrates.