Exo Terra Sub Stratum Bioactive Volcanic Substrate

The Exo Terra Bioactive Volcanic Substrate is a natural volcanic soil harvested from the mineral-rich foothills of the Aso Volcano in Japan. Formed from andesitic and rhyolitic tephra (Andisol), it is designed for keepers building bioactive planted terrariums where live soil biology does the maintenance work. Available in a range of sizes to suit builds of different scale.

What Makes This Substrate Different

This is not an inert growing medium — it contains live beneficial bacteria (Bacillus) that activate on contact with water or biological waste. The bacterial colony breaks down organic matter including animal waste and leftover food, eliminating ammonia and suppressing odours naturally. The result is a self-sustaining terrarium ecosystem that stays cleaner for longer without chemical intervention.

Structure and Drainage

The substrate's porous, friable structure provides excellent drainage and aeration throughout the soil column. Low density and high surface area support both strong root development for plants and a flourishing population of nitrifying bacteria. The volcanic ash component actively traps decomposed material, locking in odours rather than releasing them.

Three Ways to Use It

• Sole substrate: Add a layer of 1–2 inches (2.5–5 cm) directly to the terrarium floor. Live bacteria activate with moisture or waste, and decomposition begins naturally. Rinse and partially replace every 12 months.
• Drainage layer: Use as a sub-layer beneath a biological top substrate such as plantation soil. Plant roots will extend down into the volcanic layer for optimal uptake, while the top layer handles planting and surface activity. An inorganic drainage layer (such as BioDrain) can be added beneath, separated by mesh, for enhanced water flow and anaerobic bacteria prevention.
• Mixed in: Blend with other organic substrates to enrich them with key minerals including calcium, nitrogen, potassium and phosphorus. Improves water retention, root aeration and the overall microbial diversity of any substrate mix.

Ingredients

Natural Volcanic Soil (Andisol), Active Carbon, Live Beneficial Bacteria (Bacillus). No synthetic additives — the biology is built into the substrate itself.

Finishing the Vivarium

A top dressing of leaf litter complements this substrate well, providing dry surface areas, shelter for microfauna, and a moisture barrier that slows evaporation from the layers beneath — helping to maintain the stable humidity that bioactive setups rely on.

Choose the bag size that fits your build from the options above. Whether you are setting up a compact tropical vivarium or a larger planted terrarium, this substrate gives the soil layer the microbial foundation a genuinely bioactive enclosure needs.