Please do plenty of research before taking any Turtle Species on board as they live long lives, often out grow their tanks and can be very hard to rehome at a later stage.
Didn't you just start another topic a couple days ago about wanting turtles then after someone gave you a link on what you need for them and how to take care of them you changed your mind?
I had two turtles for a few years. They had no filter or anything and sometimes i wouldn't change the water for 2 weeks. For months i would feed them veggies and they never got sick. I'd say if you can keep fish, you can keep turtles.