I have a CB70 rack from RBI, can anyone tell me why my temps in the top rack are always different from the middle and bottom one? For instance, right now my top hot side is 84 and cold is 79 while the bottom and middle are both at 89 hot and 84 cold?

I would have thought the top would have been the hottest. I have a Helix thermostat set at 94 and am using a Ranco as backup set at 96, I also have a temp probe set right next to the Helix probe and that reads 96 and for whatever reason even before I purchased the backup t-stat the digital temp gauge always read 1-2 degrees higher than what the Helix was set at.

All probes are taped directly to the heat tape just to the right of the top tub and temp were measured with a heat gun from inside the hides.

Any ideas?

ETA: I am using aspen as substrate and it is as evenly layed throughout the tubs as I could have got it, if that makes a difference.