My Valentini puffer has started looking weird. He's always been a round little guy that acts like a begging dog. Recently he's started looking thin, and instead of his lighter color he's kinda dark brown. His attitude became sluggish yesterday and I put a half shelled clam in his cave so no one would steal his food but I'm not sure what's wrong with him. He has a nip at one of his fins, but all my water parameters are normal