To keep your turtle's shell healthy, make sure to provide a balanced diet that includes calcium and vitamin D, as these are essential for shell health. Additionally, create a suitable habitat with clean water for swimming and basking areas for drying out completely. Regularly inspect your turtle's shell for any signs of damage or infection, and consult a veterinarian specializing in reptiles if you notice any issues. Brushing the shell gently with a soft brush can also help remove any dirt or algae buildup.