This is the Ultimate product to create a false bottom in your habitat, it is lightweight and you'll want to use another substrate over the top of it: NZ Moss, Clay Substrate (great fortifyer for isopods, contains lots of minerals)
These clay pebbles are a unique, lightweight expanded clay aggregate it is ecologically sustainable as it is derived from a replenishable source, clay. Clay is mined, formed into pellets and fired at high temperatures to cause the clay to expand into lightweight balls that are porous but do not float like perlite. Clay naturally has balanced capillary action to accelerate plant growth with an ideal surface for root structures and beneficial bacterias. It drains freely, is pH adjusted, free of harmful heavy metals and inert. Each batch is tested before bagging to ensure highest quality. You can use it as a top dressing for moisture retention in outdoor landscapes as well as mixing in with container gardens to increase aeration and drainage. For best use, rinse before planting.