I've been rethinking the livestock and filtration. Now I'm thinking of just going with just sponge filters so as to not have a lot of current in the tank and going with fish that prefer less flow. I want corys and according to Seriously Fish, Corydoras Habrosus (Salt and pepper cory) prefer areas where the water flow isn't strong.
Rasbora sarawakensis (Blue line rasbora) seem like good candidates. Maybe Nannostomus marginatus (Dwarf pencilfish). Possibly Trigonostigma heteromorpha (Harlequin rasboras), a mix of the red and purple varieties, but they might need a little more flow.
I'm interested in trying out all sponge filtration. I know the sponge itself acts as a bio medium. But I want the kind that has an extra compartment for bio beads. And either has a bubble disfuser built in or something I can rig with an air stone.
If you have plants as mentioned earlier in this thread, you do not need much filtration, a dual sponge would be enough. The plants are doing the nitrifying, not bacteria. The water flow is a separate issue though usually connected to the type of filter to avoid clogging the setup with extraneous equipment. I had no issues with a 29g tank with a dual sponge filter (pictured), with nano-type fish, hatchetfish, and a group of pygmy cories. But moving up one grade, if I felt the need for more water flow, I then turned to an interior corner filter like the Fluval "U" series or the Aqueon Quiet Flow pictured below, that is basically a sponge with a motor. You again do not want "biological" filtration as this is the job of the plants, and in any event it will occur regardless of the filter, even when there is no filter.