Here's a new how-to guide on making terrariums at the Michigan live website. The how-to focuses on creating sustainable ecosystems within terrariums to foster long-term plant growth. The article suggests using clay pellets as a purification filter for the system instead of charcoal as the pellets are supposed to last 3 years or more and charcoal can "wear out." I have never heard of these clay pellets- has anyone else had any experience with them?
Many terrarium tutorials suggest adding a layer of charcoal to keep odors at bay, but local experts say the charcoal only works for a couple of years. If you plan to maintain your terrarium for longer, substitute a layer of fired clay pellets. These are commonly used in place of dirt in hydroculture systems.
Making Terrariums at mlive.com