terrarium for mountain horned dragon

Cocoa fiber is the shell ground up. Eco earth, and.... I cant remember any other names. I wouldnt depend on coconut fiber/shell to breakdown the waste, as it's not soil and does not contain any of the needed bacteria and fungi. Coconut bark has to be changed out and spot cleaned, or else you risk harmful bacteria and belly/scale rot.

Pick up the book , read it, I really think it's what your looking for. I can't imagine it being any easier through trial and error while you have an animal living in the enclosure. He's very thorough in the book.

Any soil will have good bacteria and fungi, and harmful bacteria and fungi. It's up to you which route you want to try. Just know that many potting soils do have chemicals, so look for organic, chemical free soil.

Also, with an animal as large as a mountain horned dragon, I don't think you're going to be able to rely on the bacteria in such a small enclosure to break down its wastes. There will just be too much for that small ecosystem to handle. You'll have to spot clean it, so don't worry too much about the substrate except for the plant's health and humidity.

Mixing your own is a good route to go. Exo Terra sells a few that are good if you want to mix. One is called Jungle Bedding. You can mix that with some fertilizer free potting soils that are rated for terrarium use. A lot of garden centers will sell it. Make sure to stay away from anything with Peat Moss. It rots. Good luck!