The compact h 2 phase bio internal filter requires the following filter media 1 x poly pad 1 x carbon sponge 2 x filter sponge coarse 2 x filter sponge fine poly pad poly pads are designed to absorb larger particles of dirt in the water when the particles are caught by the pads they are prevented from obstructing the growth of water cleansing bacteria change poly pads weekly or more often if you have large or strongly burrowing fish carbon sponge the carbon sponge cleans the water f