The bacteria can double their population in under 24 hours so once you have a good start the time factor becomes quite small. Say you start with enough bacteria to serve for a 5 gallon tank, next day you have enough for a 10, next day enough for a 20, next day enough for a 40. You can see where this is going.boshk said:some say its really quick cycling a tank with established media, like a few days? You just need to provide the right conditions for the established bacteria to reproduce itself to the correct amount.