as far as potting soil... its what I had on hand and i made sure no insecticides or fertilizers where in it before hand. (side note, I spent 30 min talking to folks at lowes the other day wondering why they didnt sell any perlite that didnt have miracle grow added to it)and i always freeze substrate for a few days before it even enters my snake room.

in the future i'll get a more natural soil source. there is a small stream running in a field next to my house that has some natural sandy soil so i've thought about getting some buckets of that. i've just held off because its also a little clay heavy and I worry about it being to hard of a substrate... i guess mixing stuff with it could balance it out though.