Rack temps

[Ascended]

My guess is their heat tape is one continuous piece so it is on one tstat. That is how I mine is.

Ahh, I see. Heat tape is hard to come by in the UK. I use individual heat mats. (mini heat tape I guess)
But what about the problem of heat rising?
The top will be always hotter than the bottom in a 7 high rack as stated here. Its just how heat works (shoot your gun at the floor then ceiling, there is a few degrees difference) . Unless you have incredible air circulation with serious fans and brilliant insulation in the racks.
That's why I use 3 thermostats minimum. The various levels are not the same otherwise.
In addition to heat rising - the bottom one has no bottom heat from the tub below, so even more cooler than just the heat rising alone.
Maybe I am being too precise. I guess a few degrees difference may not make that much difference.