10 degree differences between levels of a 2 level rack is definitely not normal. Even on my first rack I built many years ago, when using an inferior thermostat to Herpstat, I had only a 8-9 degree split between the top and bottom shelves of a 10 level rack. There should be only a couple degree difference between your two levels. Flexwatt is notorious for having uneven heating, and depending on how the rack was wired that can complicate issues as well.
I agree with others that the temp should be turned down to avoid overheating the top tub. A 90 degree hot spot isnt even necessary. If there is still variation between top and bottom temps, maybe try to get the lower level in the mid 80s, and then hopefully the upper level will be no more than low 90s.
Reply With Quote