This is a magnificent beast, but he's a terrible photography subject.
His environment is a 40 gallon aquarium, with a fake floating log where he can bask under the right lamps to provide him with UVA and UVB rays, so his shell hardens correctly. So, when he is above water, he's being hit with bright lamps, from above, with a bizarre color which I find hard to correct for. There is too much yellow, obviously, but every time I attempt color correction I can't get it right. So here he is without color correction.
When he's under water, he's in a reduced light situation, which is also a rather unnatural light. He's also moving nearly 100% of the time. Auto focus lands on the outer aquarium glass half the time, and the rest of the time is searching for a moving object in low light. Flash is always too bright and creates something unnatural in an aquarium.
The subject is also surrounded by reflective glass to make everything just that more difficult.
But the most difficult problem is that I'm finding my flawed amateur shots don't communicate what I think is cool about him. He's built to survive, secretly the most badass animal in the pond. He basks in Superman formation, legs straight out and arms back to capture the heat of the midday sun. In the water he's a floating saucer, swimming by rotating his enormous rear legs like canoe paddles. He examines the world above the surface by poking just the tiny eyes and nose out, 1% of his body. His throat expands to capture a balloonful of air, and he's back diving again, good to go with the protection of the water.
This is a magnificent beast.