PACKAGE CONTENTS - 6 x Filter Sponge. REPLACEMENT FREQUENCY - It is recommended to replace the filter sponge every 2 months, one piece at a time. PRE-FILTER SPONGE - The filter sponge works as a pre-filter to knock out impurities, including uneaten food, fish waste, and plant debris, thereby preventing the reduction of light efficiency due to waste accumulation on the glass sleeve. ROUTINE CLEANING - Depending on your tank's environment, clean every 2 weeks. To clean, simply remove the filter sponge and rinse with clean water. Aquarium filter sponges(6 PCS) for fish tank filter.