Turtles and outside temps

[Naomijoy]

So apparently I've become the person that people give their unwanted turtles to. I don't mind all that much...I like turtles Here is my question:
I've put together a stock tank pond for the Slider and the Pinnensula Cooter. I'm wondering at what water temperature they can go in the tank? It's an above ground pond that is about 120 gallons.
Also, I have an African Sideneck. Can he go outside in the summer too? I live in Minnesota so I'm pretty sure outdoors in the winter is out of the question, but that's ok. I just don't want to shock his system when they go from room temperature water in the house to the outdoor tank/pond.