It's a good news, bad news day for the aquarium. I finally got all five kuhli loaches into the fish trap to feed. The black ones still enter first, two striped kuhlis were in there when I checked five minutes later, and the last one shortly after. So they're learning! Each time find the way in quicker.
QT, at the very least I can keep their water super clean with extra water changes there. Am asking on the fish forums. It could be bacterial, from injury? or fungus that attacked the injury when my filter was out, or columnaris (god I hope not).