Supplements for Your Box Turtle
Your turtles really shouldn't need much in the way of extra vitamins and minerals. If you're feeding them a varied diet, they should be getting the nutrients they need. One exception is calcium. Calcium deficiency can cause death and deformity in turtles, especially hatchlings. Since calcium is so important to turtle health, supplementing this mineral is a good idea.
Reptile Calcium Supplements
The easiest way to give your box turtle extra calcium is to sprinkle powdered reptile calcium on her food before each feeding. To coat live food, like mealworms or crickets, put the insects and a little calcium powder in a bag and shake. Use a calcium powder without extra phophorus.
A piece of cuttlebone in the pen can also add extra calcium to the diet. Having this source of calcium freely available also allows your turtles to self-regulate their calcium intake. This can be especially important for gravid females.
Rep-Cal, Herptivite and Reptivite are all good brands of reptile calcium supplements.
Reptile Vitamin D Supplementation
Just like humans, turtles need Vitamin D to metabolize calcium. If your turtles spend time outside, they make this vitamin on their own when their skin is exposed to UVB rays.
If your turtles do not spend time outside, it's a good idea to use a calcium supplement that also contains Vitamin D. You do wan to be careful when doing this, becuase turtles can overdose on Vitamin D.
Reptile Vitamin A Supplements
If your turtle has peeling skin or swollen nictitating membranes, it might have a Vitamin A deficiency. This usually only happens if he is not getting enough plant-based foods. Before resorting to supplements, increase the amount of dark leafy greens and yellow or orange vegetables. Adding a drop of cod liver oil to the food can also help.
Since these same symptoms can be caused by dehydration, too, try increasing the humidity in the habitat and making sure the water bowl is clean and filled.
Only if changingthe diet does not work should you consider supplementing with vitamin A, because it's very easy to over dose with this vitamin. Too much vitamin A can damage your turtle's liver, which can lead to problems absorbing calcium.