Single wall climber

I have 15 crystal reds and blacks in my 10 gallon planted tank. Parameters are good, I’ve got three berried ladies, everyone seems happy — except one male who spends a not insignificant amount of time running up the walls. Sometimes he goes up to the surface and bops up there for a few seconds, sometimes he just speeds around the tank. It’s been a few weeks of this. I don’t think it’s the water unless he has different preferences from the others. Could it be some other problem?