The Exo Terra Calcium and Vitamin D3 Powder Supplement contains high levels of phosphorus-free calcium, as well as balanced amounts of vitamin D3 for optimal calcium absorption. Calcium deficiency is a major dietary problem in captive reptiles and amphibians. The Exo Terra Calcium and D3 Powder Supplement aids in providing proper amounts of calcium to your reptile or amphibian. It is vital for captive reptiles not exposed to natural sunlight or ultraviolet lights to have Exo Terra Calcium and Vitamin D3 Powder Supplement included in their diet, since they do not receive the proper amount of Vitamin D that other reptiles get from the sun or ultraviolet lights. The Exo Terra Calcium and D3 Powder Supplement is a complementary food for reptiles.