Substrate Question

New to pods, have cubaris murina papayas and eventually going to add a grove snail to enclosure. I am using coco coir mixed with eggshell, worm castings, and spagnum moss. I have a moss pile on the wet side and leaf litter / rot wood covering the floor. Last post I was told to add some more substrate, so I got topsoil! However, a friend told me coco coir is deadly for isopods, can cause impaction, replace completely with topsoil.

I'm getting conflicting info from the internet, what do you guys think?