I wish to redo my terrarium. What exactly is activated charcoal and where can I purchase in the Toronto area?
Activated charcoal is a highly porous type of charcoal that acts as a filter in aquariums and is used in terrariums. Usually you start with a layer of pebbles at the bottom of a container. Then spread a thin layer of the activated charcoal (about 1/2 inch) on top of this base. A layer of sphagnum moss is recommended next and then finish up with about 2ins. of potting mix. The activated charcoal will help eliminate chemicals that might seep into the potting mix and prove toxic to the plants. It also keeps the terrarium clean and fresh smelling and stops fungi from forming. Activated charcoal is absolutely necessary if the terrarium is sealed.
Sometimes this product is referred to as horticultural charcoal, gardeners charcoal or activated carbon. It can be found in aquarium supply stores, specialty flower/garden stores and reputable garden centres. Charcoal used for barbecues is not recommended.
Further information on terrariums can be found at https://extension.missouri.edu/explorepdf/agguides/hort/g06520.pdf.