I recently added some fresh wet Moss into my terrarium, and with it came a strong smell. The smell went away pretty quick, though. Maybe a couple of hours or so. Do you make sure to look for and clean up any mess that your pet may have left? I had just recently cleaned the terrarium, so all I did this time was added some fresh plantation soil (brick) and tilled what I already had in there. I think that helped to get the smell out as well.