Mississippi map turtle shell issue

[bman7842]

I have a Mississippi map turtle. I got her from petco and I have had her for over 4 years now. Just recently this sorta white reflective stuff has started to grow on her scale. You can only see it when she is in the water or it is easier to see it in the water. I have never used any special sort of shell grow kit like vitashell or whatever it is called. She basks daily and the basking area is the proper temperature. I have both lights needed and she gets ton of natural light for her shell with no glass blocking the rays either. The shell is also not squishy in the areas that have this white stuff. I tried brushing it off but it did not really help. If you gave any idea on what this is please tell me! Thanks!

This is an image of her,
20150219_191316.jpg

[mushiducky]

I used to have common river turtles and they had this issue as well. Perhaps it's due to her diet intake?

[Therry92]

I wonder if it could be an infection or some sort