My first dart tank. (pic heavy)

[pinkfeet]

has anyone used the heating pads for there dart tanks. iv found with the cold weather we have had lately that the temp in my new dart tank is not so consistant lately. lower level is high high humidity but the temp is steady at about 68. where the upper level is a steady 75. any recommendations? should i get a small heat pad to place under the tank? if so any size or brand suggestions?