I've got my thermometer now against the plastic under the substrate. It's reading a constant 91-91.5 which makes me feel much better than 73-75 admittedly. I just wish I could get the temps perfect. Does ambient temperature in the room make a difference? The room they are in is a bedroom at the moment and stays at a constant 73-75 as that's what makes me comfortable. Would I be better off putting them in a different room and turning the heat up to 85 or so?