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So currently, I am thinking about setting up a 20 gallon freshwater tank with serpae tetras. I already have a sponge filter that has been sitting in an established tank for a while now (a month or two). I was planning on setting up the tank with this sponge filter. I heard you can instant-cycle tanks this way, but I would like to know whether or not this is true. I also have a mechanical filter called the Aqueon Penguin (at least I think that is what it is called). Would I be able to cycle this mechanical filter with the established sponge filter? Some people say to squeeze the sponge filter into the tank water to help seed other new filters. Should I do that? Also, how many fish should I start out with (if the tank is ready for fish). Would two or three serpae tetras to start be too little or too much for the filters to handle?