If I use a substrate, I usualy make a naturalistic vivarium. If it's to be planted, I put at least an inch of pea gravel in the bottom to act as a resevoir for water, and promote drainage. Then, I put a mix of potting soil (without pearlite), often mixing in a little orchid bark to change the texture. Then, I cover about a third with carpet moss. I have used this method for frogs a lot, and it keeps the humidity high, while giving adequate drainage.
Mold means you have a high humidity with very poor airflow. Mold is oportunistic, and wont appear if you do two things:
1) let the water evaporate, just replenish the level in the gravel by watering the tank (some old timers used cheesecloth between layers, but I find it limits root penetration)
2) Air it out - if you have a perfecto lid, break out the rear parts where they are scored, and replace with screen. Or, better yet, use a screen lid and partialy cover a portion of it to reduce airflow - only if needed!
Watering your plants from above helps break down the waste, while the soil holds the bacteria needed to break it down.
That's how I do it.
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Paper products - and some plants - contain compounds that mimic the juvenile hormone, part of the biochemical pathway to the molting process, and have - in some insects - been shown to delay development. It's called the "Scott Towell" effect. I swear that I am not making this up...[/SIZE]
http://www.agsci.ubc.ca/courses/agro/327/A....lecture.05.pdf