HydroBalls by Zoo Med is an 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 inside a terrarium