Al seems kind of bored and lonely outside sometimes- he doesn't get as much human interaction as he did when he lived indoors. I am not sure, though, if the pond is really big enough to add another turtle. It's a 150-gallon stock tank, filled to about 135 gallons of water.
If I were to add another turtle, it would be a male YBS. I get the feeling, though, that there's just not enough room in this tank for another turtle. What do you think?

