maybe a red tail chalceus. . . . it's like a giant tetra.
That's a pretty good thought, which I will consider. The two drawbacks I can think of is, as a fast swimming, active predator, it might outcompete my ambush predators, and that it's fundamentally a schooling fish, so I would hesitate to keep a single one just like I would hesitate to keep a single neon.
But for all that, it certainly bears thinking about.