If you already have Buenos Aires tetras, this may be moot, but because I am anal about geography, I would think Congo tetras would be a better choice, as they come from the same area in Africa.
They also grow large enough, that even when the Ctenopoma gets full size (@8") the Congos would (by then) also be too large to swallow.
At full size (for the Ctenopoma) the Buenos Aires tetras would be bite size, and since the bush fish is an opportunistic lie in the weeds stalker, striker, as opposed to a chaser, its speed might also be a moot point.