Kuhlis do best in large groups, otherwise they hide and you never see them. I'd say with a well-cycled tank and regular water changes, you could do 4-6 kuhlis. Although they have a maximum length of 4", they're so thin that their bioload is fairly small. They're also prone to swimming up and out of even the smallest hole in the tank lid so use saran wrap to cover up any holes. I found my cat batting one of my kuhlis around under my dresser. Surprisingly, it was still alive. I picked it up, pulled the cat hair off, and put it in QT. It survived.
Thanks. I'm trying to remember who used what. I'm, trying to establish my cycling credibility over at TFK. I'm appalled at the misinformation and out-of-date info that these "experienced" keepers possess.
Other than I think they're cool, I don't know anything about Kuhli loaches. Sakura8 does. So does Olympia, I think.