The funny thing is that none of the Kuhli loaches that I keep in my 10 gallon ever glass surf. However, the ones I have in the 40L are out all the time (not just at night when the lights are out) swimming around and glass surfing on occasion. In over 40 years of keeping fish, I've learned that fish do what they want, when they want and no two fish of the same type have to act the same. Getting different results than what is the accepted "normal" happens all the time. That's what makes this hobby so much fun.