Tortoise shells are susceptible to getting bacteria or fungal build ups due to living on the ground and residing in moist areas. Signs of typical shell rot will be a white powdery substance on the plaston. A two-step process of cleaning the shell with Hibiclens followed by keeping it clean with Betadine should be repeated for a few weeks. This process should be done daily until signs of fungus are gone. In extreme cases, the shell will need to be scraped or dremeled to remove the buildup (we highly recommend consulting an experienced veterinarian before proceeding this far). The tortoise shell will regenerate over time and proactively cleaning the tortoise’s shell, works as a good preventive.