You can go as complex or as simple as you'd like to with your isopods' substrate. If you use an organic, nutrient-rich mixture, you won't have to feed them as often because they'll live off the decaying matter. If you use something simpler, like coconut fiber, you'll need to feed them every couple of days.
Here are some common ingredients for isopod substrate mixes:
- Organic topsoil (base/bulk)
- Organic potting soil (base/bulk)
- Coconut coir (base/bulk, moisture retention)
- Peat moss (base/bulk, moisture retention)
- Sphagnum moss (moisture retention)
- Organic compost (nutrients)
- Vermicompost (nutrients)
- Charcoal (odor control, aeration)
- Orchid bark (aeration, roughage)
- Leaf litter (nutrients, roughage)
- Calcium powder or powdered oyster shells (calcium)
On top of the substrate, consider adding a few pieces of cork bark or decomposing oak bark. Isopods love to consume rotting wood, and it'll offer a great space for your isopods to congregate and seek shelter.