Diamondback Terrapin

Just in case any of you wanted to see one of these guys:
This one was rescued from smugglers along with two of it's siblings, one of which unfortunately passed soon after.
This one is housed in a 6×2×2 aquarium with an overhead area of the same dimensions with about 4 feet of land and 3 of those are fully artificially planted.
This one is very interactive!
Edit: forgot to say, this one is housed in a rescue and rehabilitation center, pretty big part to leave out, oops

 

So tank mates?

 

It had three tank mates, all different species, but I have no idea what kind of fish they were

 

I think you should get 33 neocardina shrimp, 15 apple snails, 30 guppies, and 30 mollies. Put some crates with holes big enough for the fish and inverts to get in but not your turtle in the tank, put live plants in and boom you just created a self sustaining ecosystem. You like?

 

That would be cool, but this turtle isn't mine, sorry.
It's pretty illegal to have one of these, at least in the states.
That's a really great idea though, if I ever do get a turtle, I'd have to at least try it!
I edited my first post, because I didn't make that clear at all, oops

 

Is that tank yours? If so, you could get a couple red ear sliders. Sorry just read your edit, you should get a tank that size

 

I'd love a tank that size, but unfortunately my biggest is a 60 gallon, and I don't think it's suitable for any turtle really... Maybe a mud turtle, but that's about it.
I really like your idea of having hides too small for turtles to get in, but big enough for fish to hide in. I hadn't come across that concenpt in any other "enclosed ecosystem" type of thing, it's a really interesting idea. I may be able to do something of that sort in my goldfish tank, but with scuds or fairy shrimp or something.