An under tank heater is not made pointless by a new substrate. If you already have a heat lamp producing solid temps then a heat pad is unnecessary in my experience. If you are using just plain eco-earth then just make sure you let dry well before reapplying moisture as I have found it to mold quickly...I prevent this and maintain relatively constant humidity by adding a small top layer of cypress mulch...it has a natural pH that prevents fungal growth. Hope that helps.