I built this thing and used it for 2 years. On one shelf. Now I added another. It is heated from the bottom. So it heats quicker at the bottom and cools off quicker. But my temps are going from 98 to a little over 102 on the bottom and 99 to 101 .8 on the top any ideals of what I can do to gt them closer together? I have a water bottle in the bottom to help with the temp.