All of the HOB filters I use just use regular plastic filter cartridges with the blue sponge material filled with activated carbon. I usually slice a small slit along the top edge of the cartridge and remove the carbon (I keep it saved in a ziplock for later use) and put the cartridge in the filter. Instead of buying filter cartridges, how can I use filter floss in a HOB filter? I was thinking about buying a filter media bag and filling it with floss, then sticking just the plastic component of an old filter cartridge down inside the bag to provide support, then sticking this in the filter. Will this work? I'm just thinking of ways to save money and simultaneously increase the filtration capacity of my filters.