Eheim Prefilter

EHEIM Prefilter 

This extra prefilter traps the majority of coarse dirt particles, even before the  water reaches the external filter.  Its base rests securely on the bottom of the aquarium. The water is drawn in all round, over a wide surface area, through the modular filter baskets which can be filled with filter media and easily cleaned and replaced. For cleaning, you simply remove the filter baskets.