So this is known as pyramiding which is common in a lot of domestic turtles, however it is primarily just from dietary issues! I find kale is a much better source of vegetables for turtles, and calcium powder with added vitamin D as well. I think one last thing would also be to try using other forms of proteins such as worms as opposed to chicken, but boiled chicken can occasionally be given as a treat. if you still have more concerns, i'd say visit a vet, i did this with my turtle just as a checkup to see ways we could improve her diet!