Mold is a common natural occurrence in bioactive enclosures and terrariums and isopod bins. Mold can be unsightly and unwanted, but it is usually not a cause for concern. It's just nature running its course.
When a bioactive habitat, isopod bin, or terrarium is first set up, mold is extremely common as the mini ecosystem is trying to balance itself out or "cycle" itself, similar to a process an aquarium goes through. Bark, wood, and other botanicals, such as seed pods, will often develop some mold when they are added to the tank if the enclosure is wet or has high humidity. There is no need to worry. The mold will eventually run its course, and your bioactive enclosure or terrarium will look beautiful in a few weeks.
There are a few things you can do to lessen the amount of mold while you wait for your habitat to balance itself out. Adding a clean-up crew, specifically springtails, will help to keep the mold under control. It's helpful to wipe off the excessive mold so the springtails can do their job more efficiently. The mold may have to be wiped away several times over the course of a few weeks. Another option is to spray the molded area with a water and 3% hydrogen peroxide solution (2 parts water to 1 part 3% hydrogen peroxide), let the solution sit for 15 minutes, and then wipe the area clean. This process may need to be repeated several times over a few weeks. In our experience, the weak hydrogen peroxide solution is rarely needed, and simply wiping away the mold is sufficient.
The good news is once the bacteria and nutrients get balanced in your bioactive enclosure and the clean-up crew gets to work, the mold will go away. Patience and a little bit of wiping mold away will reveal a beautiful little ecosystem in a few weeks.