I use a Fluval four plus and it works great. You may want to go with a slightly smaller one for your setup. I use substrate on the side with the turtle, then have a divider with the filter on the other side. This allows me to keep the water deep enough to run the filter without having it too deep for the turtle. as he gets bigger I can remove the divider and the substrate as the system will probably need to be cleaned more often. If you really want to have no substrate you could do a Fluval Two plus at either end and probably have pretty good luck and a lot of filtration.