Several months ago my red-eared slider's shell began losing the green color of his carapace in some spots, resulting in several yellow splotches (with most towards the front of the shell). I took him to a vet that had experience with turtles (he even had a 50 year old red eared slider at his office), and he seemed to think my turtle wasn't getting enough UVB light. I bought a spotlight lamp to replace the fluorescent tube light I had been using.
While the discoloration isn't getting any worse, it also isn't getting any better. Does anyone know what I could do to restore my turtle's carapace coloration? Is there a possibility the condition is irreversible?