Kuhli loaches get quite big, and are very active fish IME. During the day they hide a lot though. A 5gal really doesn't give them enough space to behave normally.
Just upgrade the size of tank, that way the kuhli loaches are being looked after properly, plus you can choose from loads more species of fish.
You could have things like celestial pearl danios, microrasboras or male endlers in a 5gal - but it's important to house the kuhlis properly.