I think you can actually make your own filter. Why not have a piece of glass running the tank length-wise and as high as you would like the water level to be. Then you can partition the new divided side in almost the same manner as a sump with a pump at one end and inlet/overflow at the other, place in a section of mechanical filtration for clear water, the rest filled with planting medium. Now you have a whole planting surface. You can always cover up the glass in the same manner as all the other DIY backgrounds.