Hello, so yesterday my brother who is moving to florida and couldn't take his daughters turtle decided to give it to my mom he/she is a red eared slider and after doing some reading I believe this poor little guy hasn't been cared for properly first the tank is way to small it's about 12*12*3, no basking light/area or water heater he didn't even have anything to get out of the water. The turtle is about six years old, which considering his circumstances is a miracle. Anyway so last night I noticed that he had some white lines on the shell and also noticed that the shell is peeling. So I'm wondering if this is possibly shell rot. Oh and they've been feedinf him one of those commercial diets, Tetra i think. Any info is greatly appreciated.
Oh and don't worry I plan on getting him/her into an appropriate habitat with everything a res needs.
Here is the link to some pictures of what I described