ok I had the same issue a week ago, I started my tank in the winter and now summer is here and I was freaking out. I was shooting to keep my tank at 78. Well it would jump to 81.2-7, Thats a huge jump in my opinion because you really dont want any change, and definatly less than 2 degrees throughout the day. So I bit the bullet and decided to raise the tank temp to 80. Now that I have it set not to go below 80, when it raises to allmost 82 in the heat of the day, its 2 degrees less of a jump.