What kind of filter do you have?
I use this with all of my penguin and emperor filters,Pond Mechanical Filtration Media: Uncut Blue Bonded Filter Pad
I just cut it big enough so it fits in the filter box of the smaller penguin filters,and with the larger filters,I bought these,Search Results for SuperCartridge
and just cut the filter pad to size,and stuff it in the cartridge.
In the tanks that have my larger,messier fish,I use this with the larger filters to add chemical filtration,Media Basket for Penguin Power Filters (Marineland)
Buying the disposable filter cartridges can get very costly over time.This is one way I have found to cut the cost of mechanical and chemical filtration.
I just rinse out the filter pad once a month of so in a bucket of tank water.I use the pads until they are literally falling apart.