I think I have the best answer, but don't we all....on a 40 B I use an Eheim 2217'with a pre-filter sponge to keep,the heavy dirt out. On the other end of the tank I use an Aqueon 30 without a prefilter sponge to suck up most of the large detrius. The Eheim holds the bio-media and course blue sponge and the Aqueon is for filtering dirt only. I have to change that out about every 4 days. I use a 100 micron pad in it.