HydroBalls™ Expanded Clay Terrarium Substrate can be used as a base layer underneath Zoo Meds Eco Earth® coconut fiber substrate or other substrates to create an underground water table in Naturalistic Terrariums. Add water to create a natural "aquifer" and increase humidity levels for all tropical species. Excellent substrate for live plant root growth in Naturalistic Terrariums. Use for filtration for a waterfall.