If you are worried about a calcium deficiency in your aquatic turtle's diet, you can supplement their meals with this Zoo Med Turtle Bone, allowing you to rest assured that your turtle shouldn't be suffering from things like MBD and soft-shell.
Made from a cuttlefish bone, it floats naturally and is packed full of calcium for your turtle, they just need to swim up and take a nibble whenever they fancy it, giving your turtle a healthy extra dose of calcium to give them everything they need to develop a healthy skeletal structure and shell.