25c to 26c. You can go as low as 23.
Sorry if the following is what you already know, but hopefully others interested in these fish might find it useful.
The Congo is enormous and gets a lot of sun, so those fish like 26. I don't know about the auriantacus. The small streams we measured in Gabon, which would be like the creeks I believe they come from are shaded, and were about 23-24. This was right on the equator, with 26 degree days. It should be the same in Congo. We weren't that far away. My return flight was rerouted or I would have flown over the great river.
The info on them says they like shade, so you may want to try to adjust to them first. As far as I know, the others are main stream Congo from different points along its length.
There isn't a lot of species flow along the Congo in many areas, because the rapids are so violent small fish can't get through without being pulled into zero oxygen depths. So you have a stretch of fast moving river, gigantic rapids, then another stretch, another torrent and so on. Each can have different species - similar, but not quite the same. The big river ones have the same basic conditions - clean flowing water, high oxygen levels.
The tributary stream fish are often darker bodied, like brichardi (maybe?) or auriantacus, as silver scales in sun are good camo, but get you eaten in darker habitats. Darker is usually a bit cooler.
Your interuptus and caudalis are sunshine fish.
You'll get people who announce fish adjust to any aquarium, because they haven't ventured into keeping fish that don't. Actual research in killies shows a 2 degree difference in water temperature in the wild equips them with different digestive enzymes, so the fish that come from the deeper forest can't thrive if they swim into a sunny savannah region. I don't know if temperature dependent digestive enzymes affect tetras, as no one has done that research that I know of, but it kind of made me wonder.
That info came from climate research, which suggests a lot of fish are vulnerable to extinction because of their specialized digestive systems.