I just realized a tiny little problem with the stocking idea. The Pimelodus ornatus would proabably eat the Beunos Aires tetras, cories, and apistos, they get up to 11" long. I'll have to check out how big their mouths are in comparison to the possibly threaten tankmates. The Beunos Aires tetras are also fin nippers, so they might go after the apistos.
In this case, I'll probably trade out the ornate pim for a pictus. I'll have to test the Beunos Aires tetras and see how they do.