The pump inside the nano cube is a powerhead basicaly and has three settings. It is set at the highest when you get it. Just reach in, disconnect the pump from the tubing, (unplug the pump first) pull out the pump and look for the sliding switch. I keep it in the middle setting, which is still fairly strong. The lowest setting is much TOO slow. Then re connect the tubing and set it back in the bottom of the chamber. Pretty easy.