I usually use peat moss but I was just poking around at a pet store one day and I found a substrate called Zilla. It is designed for reptiles, but it is a fir and sphagnum peat moss mix. Im not sure if my Ts like it right now or if its just the humidity in the enclosure that is making my terrestrial Ts go arboreal. Anyone ever heard or used this substrate with tarantulas? Any comments are much appreciated.