Ball python bedding question?

so i have switched from aspen bedding to some Miracle Grow Moisture Control Potting Mix so my snakes tank can have better humidity. i want to know if this bedding is safe... it has the white stuff in it so will my snake be ok... also why is it that when i use aspen bedding my snake pooped little white and yellow pieces but when i started using the potting soil it poop looked like a bearded dragons poop?