[Compatible with the box filter] HW-304b/404b/704b/3000/CF500 Polar Aurora 525GPH. .[ The function of the filter environment] Removes the color of water from water, smell and dissolved fish feces. .[ Package Content] 4 Sponge Biofilter Pad (1x Crude, 2x Medium, 1x Fine): Captures the most visible rash particles without restricting water flow. (Rinse and use it again). .[ Easy to install] Easy to install, do not need complex tools, just place the filter pad in the cartridge filter, save time and increase productivity. .[ Save time and money] Non -original after -s pieces. OEM meets the standards! Extends the life of other filter media. Note: Due to vacuum packaging may appear thinner, but it does not affect the effect of filtering; For sponge pads, you can keep it in water for 5-10 minutes to to its original size. Note: Due to the light and screen setting difference, the item's color may be slightly different from the pictures. Please allow slight dimension difference due to different manual measurement.