This activated carbon in 250ml - 500ml and 1 liter portions
 
Read at the bottom about "Activated carbon's purposes in a terrarium"

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Activated carbon VS Charcoal
"Activated carbon" and "charcoal" are terms that are sometimes used interchangeably, but there are distinctions between the two.
Charcoal: Charcoal is a broad term that refers to the black residue left behind when organic materials (such as wood, peat, coconut shells, or sawdust) are burned in the absence of air. This process is called pyrolysis. Charcoal has a porous structure and is often used for cooking, heating, and as a fuel source. It's also utilized in certain art applications (like drawing) and as an ingredient in gardening soils.
Activated Carbon: Activated carbon is a specific type of charcoal that has undergone additional processing to make it extremely porous and increase its surface area. Activation is typically achieved by exposing charcoal to high temperatures and certain gases (steam or air) in a controlled environment. This process creates a network of microscopic pores on the surface of the charcoal, enhancing its adsorption capabilities.
Key Differences:
Porous Structure: Activated carbon has a more extensive and more developed porous structure compared to regular charcoal, making it highly effective for adsorbing impurities.Adsorption Capacity: Activated carbon has a higher adsorption capacity due to its increased surface area, making it more suitable for applications where the removal of contaminants or impurities is crucial.
Common Uses: While charcoal is often used for cooking and heating, activated carbon is commonly employed in various purification processes, such as water and air filtration, as well as in medical and industrial applications.In summary, all activated carbon is a form of charcoal, but not all charcoal is activated carbon. The activation process gives activated carbon unique properties that make it particularly useful for adsorption purposes in various industries.
 
Activated carbon, serves several purposes in a terrarium:
Odor Control: Activated carbon is highly effective at adsorbing (not absorbing) and trapping odorous substances and impurities in the air. In a closed terrarium environment, especially with high humidity, activated carbon can help reduce and control unpleasant odors.
Toxin Removal: It can absorb various toxins and harmful substances, helping to purify the air and water within the terrarium. This is particularly useful in closed ecosystems where waste products from plants and animals can accumulate.
Mold and Fungus Prevention: Activated carbon can assist in preventing the growth of mold and fungi by adsorbing some of the organic compounds that may contribute to their development. This is especially beneficial in humid terrariums where mold can be a concern.
Water Filtration: When used in the substrate or as a layer in the terrarium, activated carbon can help filter and purify water, removing impurities and potentially harmful substances.
Soil Aeration: When added to the substrate mix, activated carbon can contribute to soil aeration. It helps maintain a porous structure in the soil, promoting better drainage and preventing compaction.
When using activated carbon in a terrarium, it's essential to choose the right amount based on the size of the enclosure and the specific needs of the plants and animals inside. Additionally, it's advisable to replace or replenish the activated carbon periodically to ensure its continued effectiveness.