I wouldn't say the current in my tank is completely unidirectional. there are distinct zones of movement that influence each other... with a big updraft off the tall rock. I will say this, the biggest difference I've seen in them is how much nicer they get along with 30 gallons of water. They fought all the time before, and kept each other from eating. Now it's pretty relaxed. Sparring is more for practice and kicks, but isn't nearly as serious looking.