Hello and Welcome. Humidity is needed. 80% with temps no lower then 80 for growing a smooth healthy tort. Please read Toms threads below in my post for doing this.
That's an interesting use for an under-the-tank heater. I never would have thought of that. What is the temperature in the little cave under the heater?
You've made a very nice habitat for your baby sulcata. Do you have a humid hiding place for him? We've recently learned that extra humidity during the baby tortoise's first year helps the shell grow smoothly and to not pyramid.
Please get rid of that coil bulb immediately. They are known to cause a painful condition for baby tortoise's eyes similar to snow blindness. For the desert-type tortoises I like to use the Mercury Vapor Bulbs for UVB. They also provide heat. And that way you can have heat on both ends of the habitat.