I'll just say this: not very effective. Maybe if you are using a 20g as a refuge for a 55g. It can help, but it's extremely tough to implement. I used to have a leiden style 10g (extremely high plants, high rate of photosynthesis, low water changes, and exporting excess nutrients and waste via plant clippings) and it's long term stability was questionable. Plus, I could never see the fish because it was COMPLETELY packed with plants.
If you're going with this idea, the general idea is the more the plants grow, the better they are a filtration. Using nitrogen to fuel photosynthesis will naturally draw more from the water. Higher lighting (i.e. sun) and more micro and macro nutrients (i.e. fertilizer) will allow them to do this at a faster rate. Also, some plants are better suited, such as the faster growing ones like cabomba, anachris, foxtail, etc. If you layer it right, with short plants medium, and tall: you will be able to get more out of it.
The lower the light requirement of the plant, the more it will get out of high lighting. A neat thing to watch is just throw a sprig of anachris in your tank (don't even plant) and watch it grow! Kinda like those pills that turned into sponge animals when you put them in water.
