I've had two adult turtles for about 3-ish years, and they're still here. My sister decided to get 2 baby turtles for herself, both of them boys. After a month or so, one turtle died for some odd reason. (probably stress) and the second turtle has been going through depression I suppose. He's not as active as he was before, barely eating. But now he is slowly becoming active again.
I decided to keep the turtle for myself, since my sister doesn't really care for it. That being said, how do I really take care for it? What do I need to do to make it happy and healthy?
(also, the baby turtle is not in the same tank as my two adult turtles.)

