Some background:
I've had my turtle since I was a little. He's around 27-28 years old. He lives in a 70 gallon tank with a large external Rena filter. The water is de-chlorinated and I add a calcium block during each weekly water change. The filter is cleaned monthly. He has a platform to bask and a Zoo Med basking light with UVA rays. The water is heated at 82F. I feed him turtle pellets and leafy greens. Sometimes carrots and zucchini.
He has never had this "discoloration" on his shell before. I am wondering if it's due to his old age or if there is something wrong.
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