Hey, so I've had my RES for about 4 years, hes in a 75 gallon tank. Plenty of room to swim as well as an area to bask in. I have both UVA and UVB lamps. There is a strong filter and a water heater (around 75-78 degrees) . I usually do a deep clean on the tank every 3-4 weeks. The environment conditions haven't changed anytime recently. He eats normally, swims regularly and sleeps. Basks like normal. I've never had any problems with him before, so I don't know what this is, maybe shell rot?
http://imgur.com/a/iW3mTo5 here is what he looks like
He started shedding, and one area in general and one section of his shell was all white. It's not soft, it's not sunken in. His shell is also getting lighter lately too. I'm just worried it's an infection. Or is the heat lamp too hot? Please help, I'll be taking him to the vet once I have some sort of an idea of what's wrong.