Posted: Thu Jan 22, 2015 2:12 am Re: new common musk!
That setup sounds all right. Be sure to check your temperatures, before adding the turtles.
As long as the turtles have easy access to the water surface (i.e., tall plastic plants or drift wood), then you can go over 10" without incident. I keep mine in 12", and she's doing great. They're far better swimmers than some people would have you believe.
A nesting area is a good idea. You can mix the sand with some peat and/or leaf litter, too. Maybe even a pinch of topsoil.