Instructions: Remove top of your 501 filter and simply replace your old sponge with this new one. Cleaning: Rinse filter sponge weekly or as needed. If your water flow (on your outtake spray bar) decreases substantially, then it is time to clean the filter sponge. Replace the filter sponge if you notice wear and tear. Made in Italy.
Zoo Med 501 Filter Media Mechanical Filter Sponge
Zoo Med 501 Filter Media Activated Carbon Insert