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.
Hey Sakura, Hal told me that you might be able to help me! I want to start a ten gallon community tank with my Plakat. I really just wanted to get some Kuhli loaches... How many can I get in a ten gallon tank?