I was just about to ask the same question. I dont want to rob this thread but heres my recent experiance. I recently had a problem when I tried to rid my tank of its aquaclear and just running the filstar canistar. When I unplugged the aquaclear and just ran filstar I noticed the same night that two of my sae jumped ship and all the rest of my fish were at the top gasping for air. I had my spraybar spraying down against the glass, so no current was anywhere near the surface. With the aquaclear there was always a current on the surface. Keeping in mind that I keep my water level high enough to where the water wont splash on the surface but stream into the tank. So I moved my spraybar to where it sprays up and against the glass so theres a current ont the surface. Does this count as surface agitation? What exactly is surface agitation? I want to try again and run the tank just with the filstar but afraid that history will repeat itself.