Seeded sponge filters serve to quickly start up a tank cycle.  An ammonia source will need to be added regularly to feed the bacteria.  Bacteria will live in the filter, on all the hardscape, and the sides of the tank.  Test the water every few days, and perform water changes weekly.  It may take a week or two to be fully established. When your test reads 20 nitrates, 0 nitrites, 0 ammonia the tank is ready for your axolotl or other aquatic pet.  If you already have a filter system, the sponge filter can be added as simply a bacteria source.  We recommend squeezing it generously into the tank.  It will cloud up the water allowing your filter to pick up and colonize the bacteria.  Keep the sponge in the tank until the cycle is complete.  Nitrifying bacteria is fragile and dies quickly during transport, add to the tank as soon as possible.