u/InterestingVisit1609

I'm trying to move 2 giant african millipedes into a larger (~40 gallon) container and need a lot amount of substrate to fill the new terrarium. I have a decent amount of creature soil/josh's frog's substrate to cover the top few inches, but not enough to fill the whole tank. I have organic potting soil that's free from any pesticides, but it does have perlite mixed in. Would it be risky to use that? It's a male/female pair so they might breed, would the perlite be a challenge to the young millipedes' survival?