So this is a canister filter?
In my short lived experience... The water that is returning from the canister, is it dispersed thru a spray bar? If yes - check that the bar is more than an inch below the surface with the "holes" pointing at a 45 degree angle to the surface... If they are facing down they will not be creating surface movement.
If no spray bar, perhaps you may need to get one? Mine came with bot a spray bar and a duck bill, I am assuming yours did too?