This tank will be filterless. To provide circulation I am going to use a Seio M620.
Thanks to the 5" substrate, I found a good place to hide the Seio.
The intake is under the substrate. I don't know if this would create problem though. I imagine the substrate particle is too heavy to be sucked in and the substrate is porous enough to allow water movement. But if it turns out to be a problem I can wrap a layer of filter material around the intake. This would also prevent shrimp/fish fries from getting sucked into the pump.