Wow, those are beautiful rocks, good choices. They should hold the heat nicely. Does the halogen blue bulb actually give off a blue light or is it a white glow? Walmart has the digital thermometers with probes for as cheap as $8.00 and also have one that is $12.00 that will give you the basking and cool side temps at the same time as well as the humidity readout. Any type of stick-on, either the strip or gauge type can be as much as 20 degrees off, so it really is important to know what the actual temps are, especially for a baby. If you'd like to see a picture of the AcuRite $12.00 digital, let me know & I will post one for you.
Have you thought about changing the sand to a solid substrate instead? It's such a concern for a little baby as they lick everything and since they poop so frequently, it's hard to clean up all the poop & liquid to try to prevent bacteria from growing. Other choices would be reptile carpet, slate, or non-adhesive shelf liner.
How's the little ones appetite? Do you need any help with the supplementation of calcium & vitamins? We're always glad to help. :wink: