Well, the general rule is:
If he's under a florescent type UV lamp, use calcium with D3 supplement
If he's under a mercury vapor bulb, use calcium without D3 supplement
However, there are some studies that suggest (not prove, but suggest)
that beardies can't really use the artificially added D3 and can only use
naturally produced D3 (from UV exposure).
So if you believe those studies then it's pointless to give D3 supplement.
Me, I'm not entirely certain either way, so I split the difference and give
alternating supplements (Mon - calcium with D3, Tue - calcium without D3, Wed - multivitamin,
Thur - nothing, Fri - calcium with D3, Sat - Calcium without D3, Sun - multivitamin).