Roop,
I too have a fluval internal and also a 55 gal tank. I used it for awhile and then ran out to my local fish store and bought a penguin 330. (Read my message under product reviews.) Even though you have good bacteria with the fluval, they dont work like bio-wheels and other bio filteration. It does move a bunch of water under the surface and my chilids love playing in the current.
By the way, do you have the 204? That's what I have... errr the 204 + rather.