Enough Filtration?

I would say going by GPH yes. But overall I say it's insufficient. I use a Penguin Biowheel 170 and a sponge filter on a 20g goldfish tank w/ 1 goldfish and 10 minnows. It's just enough. I did change the Penguin Cartridge to Imagine Bio3 cartridges which include a sponge for more bio filtration than the original Marineland cartridges. I'm not that familiar with the Cascade 200 although I do have a Cascade 700 cannister and would rate it "good for a poor man's cannister". I've become a bit partial to Aquaclear for HOB's because of the media flexibility and ease of service. And you can get stuff for them just about everywhere. Go get an Aquaclear 70 and run that with your Biowheel 170 with an Imagine Bio3 cartridge and you should have a real good set-up. ------IMHO-----

With any filter you choose make sure that the entire volume (55 gallons) of water in your tank is turned over 6 to 7 times an hour. This in turn can be interpreted by GPH rating of your filter.
For 55 gallons you filter should have 330 to 385 GPH rating.
Rohn