I've kept turtles for most of my life. I've had several red ear sliders, some soft shells, and an alligator turtle.

I had my alligator turtle for 6 years. I raised him from a baby. I didn't do anything special. I had him in a 55g tank, with two filters meant for 55 gallon tanks running 24/7 because they get nasty really quick. I had a basking area for him with a basking light and I just kept the water at room temperature, which was 75* or so. I'd go to the store and get him little feeder fish and he'd eat earthworms, too. He always ate, always pooped, and he did a lot of both.

I ended up releasing him into my dad's friend's massive pond he has behind his house. I went there about 2 years ago and saw my turtle on the edge of the pond, hanging halfway out of the water.

They're easy to take care of. Just make sure you have a really good filter, that your water isn't too cold, that you have a basking light/area, and that you feed him and he should be okay.