Calcium glubionate is the best way to supplement calcium. It's used on human babies as well as on birds and reptiles. it looks like ordinary people can buy this OTC now, whereas in the past it was prescription only. Check this for information:
Be careful to figure the exact amount to feed Monster. It could be only one or two milliliters/day to make a good dose. Be careful to not overdose this supplement.
I would buy calcium glubionate from a pharmacy, and not a pet-supplement provider.
Calcium carbonate, calcium citrate, calcium phosphate are not good sources of supplemental calcium, even though there is a huge tradition of using them in animals and humans.
Calcium deficits are caused by lack of UVB much more than by dietary problems.
The 10.0's supposedly give more of the special wavelength of UVB, without being dangerous. Be advised that these fluorescent tubes need to be within 7 inches of Monster's skin, in his basking area. Over the years I placed the 5.0's and 10.0's at 6 inches with no harm. But if they are 12 inches from Monster's skin, the chemical reaction won't make enough endogenous vit.D.
The 5.0's in the 1950's were the first source of UBV that could help iguanas make the vit.D skin reaction, allowing them to survive in captivity when kept indoors. They still work just fine if they are placed close enough to an iguana's skin (6 inches or so). It is generally thought that the 10.0's are better than the 5.0's, but there is no proof other than the manufacturer's claims. I have to read up on this again to remember the exact way UVB works to make calcium available to the iguana's bones and nerves.