Flyfisherman said:
Stick with what you have and add a powerhead - my personal choice would be to have two filters as I would want to filter all my water - not to filter some of the water and push the other dirty water around.
This is a bit misleading IMO. You
are filtering all your water when using a powerhead alongside a filter. Typically a decent power filter will be rated to at least 3-5 times the tanks volume per hour which means, on average, all the tank's water is being filtered every 12-20minutes; hardly dirty water! Also if you are using media with a high surface area (I prefer sintered glass and expanded ceramic media as I believe they offer a huge surface area combined with a wide range of microhabitats within and on the media promoting a wide range of microfauna in the filter) then you have more than enough potential area for the micro-organisms that reduce the biological waste your tank produces. Coupled with large regular water changes to remove the end products and waste too this means the tank's water is more than clear enough.
Therefore a powerhead isn't pushing dirty water around and the only function of extra water movement is to move the CO2 and nutrients around (and keep debris in suspension). The only reason, IMHO, for using a second external (unless you have too small a current filter that isn't up to the job of filtering the water) is because you don't like seeing the circulation pumps in your tank. If that's the reason you want another filter then fair enough, but I doubt you really need one to boost the filtration - just the flow.
I actually prefer circulation pumps as, because they aren't needed to be kept running 24/7 for filtration, they can simply be dedicated to the job of moving the water (and with it CO2 and nutrients) around the tank and even be turned off when the lights go off to give the fish a calmer environment overnight. They are also much more energy efficient to use to move water around at zero static head with almost no frictional loss of flow at all.