When starting to cycle your tank with our One & Only Live Nitrifying bacteria the directions on the back label say to remove the filter sock, if you have one, from your aquarium for 48 hours. It seems many people don’t know what a filter sock is and are confusing it with the filter pad or sponge.

The first picture below shows a filter sock in a holder. Typically, filter socks are used in a sump below the tank but there are holders that fit on the top rim of the tank and the filter sock sits inside the aquarium. Filter socks are a type of mechanical filter – they strain particles out of the water. The big difference with filter socks versus filter pads and sponges is that filter socks are a very fine form of mechanical filtration, typically starting at 400 microns (0.016 in), while filter pads and sponges don’t provide such fine mechanical filtration.

The reason to remove the filter sock is that we grow the One & Only Nitrifying bacteria on a small particle because nitrifiers want to stick to a surface. This keeps the bacteria in better shape and ready to start working once you pour them into your tank. But this also means that the fine mechanical filtration of the filter sock may remove the bacteria from the system so better to remove the filter sock and let the One & Only Nitrifying bacteria find a place to settle in the bio-filter media.

Photo 2 shows a typical filter pad that fits into a hang-on-tank filter. When cycling you should leave the filter pad in the filter. A filter pad like this does not provide as fine mechanical filtration as a filter sock and will not trap the nitrifying bacteria. The same with a sponge – keep it in the filter when cycling.