Calcium Turtles need calcium to build healthy shells and bones. A cuttle fish bone in the tank will be nibbled on by most turtles and supplies extra calcium. Get a new bone, when the old one get slimy! There are also calcium supplements specially for reptiles. * Vitamin D3 Synthesized in the turtle`s body using natural sunlight. A Reptile light with the appropriate ratings for UVB is recommended, or a supplement can be fed. There are supplements available that contain Ca/D3. Of course, the best way for your turtle get D3 is to get unfiltered sunlight, and then it will synthesize the vitamin. * The calcium to phosphor ratio of foods is important, as the more phosphor there is in the food, the less calcium can be absorbed. 2:1 is a good ratio. To find out more about this click here.