I am growing 3 types of Peperomia in coconut fiber right now. All I did was mix in worm castings for fertilizer and they are growing like mad.

I do not plan on changing it out anytime soon. More likely I will be adding some worm casting tea to enrich the coconut coir a little. Might add some iron in there by burying some laterite by the plants but that will likely not happen until I make a larger terrarium and then i will add it as a layer for the plants that the frogs will never come in contact with. Again, once it is in there I am not sure I will see a reason to change it out for at least a couple years. I might even add in some peat moss but only for some nutrients. Coconut coir will be my main substrate unless I find something I think is better.

Pathos and maybe another vine or two will be my main choices along with the Peperomia in whatever I build.