It could be two things. When the slider grows in size, the shell also grows, and occasionally the turtle will rub its shell on rocks to scrape off the older smaller skin. This is not as visible as when a snake sheds its skin, but a similar process.
Secondly, your turtle does not have the nutrients in the feed that it needs (RESs need protein, veggies) and the temperature that it needs, which is making it's skin too dry and soft.
Make sure you're feeding your pet a balanced diet, there's lots of resources that can help you, and pet store diets are also available although not the best option. Secondly, make sure that it has a comfortable environment. It will need warm water, a UV bulb, and a rock it can climb on to bask under.
If the shell is still looking unhealthy, go to your local vet and they will prescribe vitamins or supplements.
Secondly, your turtle does not have the nutrients in the feed that it needs (RESs need protein, veggies) and the temperature that it needs, which is making it's skin too dry and soft.
Make sure you're feeding your pet a balanced diet, there's lots of resources that can help you, and pet store diets are also available although not the best option. Secondly, make sure that it has a comfortable environment. It will need warm water, a UV bulb, and a rock it can climb on to bask under.
If the shell is still looking unhealthy, go to your local vet and they will prescribe vitamins or supplements.