The premium activated carbon (charcoal) from urbanjngl is an excellent addition to the drainage layer of your terrarium. Activated carbon removes unwanted metals, pollutants, and odors from your closed or open terrarium. Spread a thin layer over the bottom layer (sphagnum moss, hydro pellets, clay substrate) before adding soil on top of the activated carbon. Using activated carbon in your terrarium reduces odors and filters the water in your closed ecosystem, making it cleaner for the plants and the entire ecosystem.