I have maintained this species, Carnegiella strigata, for many years, it is my favourite of the hatchets, especially the "fasciata" form [the two forms are illustrated and described in our profile].
They do tend to remain fairly quiet, but when the mood strikes them they will suddenly play, sometimes in a pair, or more a group. "Sparring" as I term this behaviour in the characins. Two of them circling each other so rapidly you can hardly see them also occurs.
They will normally avoid bright light if they can, so that is fine. And also water currents; many articles still mention how this species supposedly prefers (and needs) to stand in a swift current, but this is not accurate; they do not like currents. Mine have always remained closer to the opposite end of the tank from that where the filter outflow is positioned.
Floating plants are mandatory, but make sure there is open water between; this is where Water Sprite is so useful. This species generally prefers open water if it can find it. Most probably because it naturally feeds on insects that fall onto the water surface.
And, get a few more if you can. This species needs larger groups, I would say no fewer than 9, but more if you have the space. Mine were at their best in groups of 20+. I noticed less activity when they were in smaller groups around 6-9.