I have a similar question. My tank has a UTH on each side and together the cover a majority of the bottom. If one of them is around 78 and the other around 88-90 should I still attempt to keep ambient temps in the tank up as well. Right now the room is about 70 degrees and the ambient temp is around 72. Just curious since almost the entire surface of the tank bottom is 78 or higher? My breeder said with this type of set up the ambient temps aren't as important as long as they are above 70.