I have a baby hatchling Hermann's tortoise. I have been keeping him on paper towels for nearly a month, then decided to change to sand/dirt mixture as it seems everyone is recommending it. The tortoise started nibbling on this substate. Should i continue to kep him on it and hope he will get used to it or should I remove it? (I put paper towels on top so he can't eat it right now, but he seems to be searching for it.) Would this dirt mixture hurt him?