heat tape not big enough?

[PitOnTheProwl]

I have it turned off. Because the "pulse" was not enough to keep it remotely hot.
My temp probe is not in a tub it's in the middle rack half way in the middle

Pulse is more stable that on/off........

Middle of the rack still doesn't answer any questions?????
On the middle shelf?
In the middle of the shelf??
You might be better off posting a photo......

The exact location of the thermostat probe is where? On the shelf material OR on the heat tape itself?
What are you using to measure the temperatures?
Where exactly are you taking the temperature? Under the substrate or on top of it?