Water Clarifier Help!

Most 'clarifiers' are supposed to make whatever is causing the cloudiness (algae, bacteria, dust etc.) in the water to stick together, creating particles large enough to be filtered out of the water mechanically.
Do you use floss or very fine foam in your filter? If not, that might help - the finer the filter material, the more likely the little particles will be filtered out. If it's a bacterial bloom, I doubt the clarifier or floss will do much - bacteria are REALLY small and the only thing I know of that's fine enough to mechanically filter out things that small is diatomaceous earth (a diatom filter can clear a tank of particles down to one micron in a matter of hours or even less - they're expensive, but they do an amazing job). If it's bacteria in a newly set up tank, the problem will likely go away by itself very quickly (often overnight) as your tank matures. If it's an algae bloom, you could try blacking out the tank for 48 hours and doing a water change. If it's dust (say from gravel that wasn't washed quite enough) water changes should help take care of it. I wouldn't worry too much about it as long as your fish seem unconcerned.

For a 20 gallon, the Vortex D-1 will work just fine for water as clear as fresh air! If you plan on getting a larger tank in the near future, go for the Vortex XL!