I'd like to know this, too! Been reading a bit about making terrariums but haven't done it yet. Even have a couple plastic salad containers full of mosses for when I finally do.. Anyways, I was curious about calcined diatomaceous earth (oil-absorbent) as an option instead of turface for this application. Not sure what aquarium fans think of it but it's a popular sub in "Al's gritty mix." You maybe know already, but he mixes turface with other stuff to promote drainage in containers since it is soo absorbent otherwise. Ok for water plants I guess. Also, Al says that "DE has a pH of about 7.0, while Turface comes in at around 6.2." So that could be a factor determining between the two, supposing it was alright.
Pagan, what growing medium is in your terrarium now? I'm imagining a Frankenstein/Miller-Urey sort of experience. Did you (and might you w/ turface) add activated carbon?

Me again.. Well, in the 6th follow-up where I'm linking to, Nil13 writes "I use Turface, which is similar, in my terrariums to great effect." Maybe send him an email or.. he'll show up here?

Here is a link that might be useful: Activated Charcoal: Is it absolutely necessary?

Hi Liligoat. I found that thread as well, but it was unclear to me whether Nil13 was using turface instead of charcoal or as planting medium. My plan was to use sifted turface all the way.

Right now, my terrarium has pebbles at the bottom and a substrate of potting mix and vermiculite. It's had slugs, bugs and now worms. If a velociraptor shows up there, I wouldn't be shocked.

Anyway, I have not come across any new information since I posted this query here and decided I'll just do it and find out for myself. Since there will be no organic material in this sealed environment other than the plants I will most probably eventually kill, I have this notion of the experiment being closer to hydroponics rather than terrarium building.

What are your plans?

Pagan

That's so weird how you got critters. You could say that they're completing the micro-ecosystem. :) Wonder if anyone intentionally puts worms in theirs..
Really hope the turface works! Have you seen anything about using straight turface in a hydroponic system? That's a neat concept to have a hydro-terrarium. Hydrarium?
My plan was to make a pair of open terrariums for venus fly traps. They needed transplanting from the pot they came in: two in a tiny one with long fiber sphagnum that had a bunch a algae on top. Used wide glass vases, put pea pebbles and some charcoal on the bottoms, and used about 75/25 chopped sphagnum to vermiculite as the substrate. Well.. they died. Thought I either broke too many roots or they got too hot in the sun or they didn't like the substrate... but then my mother said she might have killed them by spraying with epsom salt solution.
So the next terrarium project is just for moss and I'm going to try the DE. I'll let you know how it goes.