Hi all,
I like the Eheim Aquaballs as well (haven't tried a Eheim biopower yet), but if you don't mind a bit of DIY its difficult to do better than a "Maxijet 400/600/900" powerhead and 12" x 4" x 4" ppi10 "Koi" sponge, cut into 3 (4" x 4" x 4") cubes, with a plain white ceramic tile siliconed to the bottom section.
I've drilled cut outs some white domestic waste pipe in 4", 8", 12" lengths, with the end siliconed to a tile (as the inserts) but you can buy these ready made, or just tie the top and bottom of with a cable tie. The Maxijets come with a strainer attachment you can use as a scaffold.
cheers Darrel