I have 3 blocks of 7-8 liter zoo med coco fiber already and I need something else to add in for Codas bioactive Lay bin. What else should I add that would hold a tunnel? The Pet store that I live right next to has Zilla Jungle Mix, Eco Earth Loose Coconut Fiber Substrate, and Exo Terra Plantation Soil. Or Could I just Add Playsand? I’d love to hear your input! Thanks!