Planted Tank Enthusiast
Join Date: Nov 2003
Location: Vancouver, B.C.
You want the mechanical filtration (sponges, floss, etc) to occur prior to your biological filtration. This allows the biological media to remain clean, as the water hitting it is technically already mechanically filtered.
Also, you want to have the coarsest mechanical filtration (sponge with the biggest diameter cells) first, so that it captures the largest matter first, and then have the medial progressively become finer as you go up the filter usually ending with floss for the finest particles.