Wow, that is actually surprising to read of this, thats a real shame as I do like the look of those tetras to be fair and if had the right water requirements, would have seriously considered getting those.Really regret buying those aphyocharax nattereri, the internet greatly understates the sheer conspecific aggression in this species. I would compare their behaviour towards characin to exodon paradoxus. It was incredible honestly, they killed pretty much all my hyphessobrycon wadai overnight and I have only a few blue ribbon left, despite the significant size disparity. I've had dominant males in the group leave water as they're chasing eachother, individuals have their eye ripped out only to immediately attack another fish moments later, and plenty of other aggressive behaviour. They've reduced the group size by 10 from fighting.
Sorry that has turned to be a regret and the loss of some of your other stock is not great news.
Good news in getting to swap those out for stocking you prefer to have.
Good luck with the new lighting, hope that works out.