That does work, but it has to be in there for awhile. I cycled a qt using three sponge filters from my display and another qt that were all about a year old (in tank) and still had a mini cycle. It was a very small cycle that only lasted two days though. I am sure they do not have to sit for that long, a month should do it. That is great though for people that do not have room to keep a qt set up all of the time.