HOB has 3 sponges, two are newer that I was establishing for setting up a new micro tank, 50 micron cloth, Chemipure easy green, and fluval biomax that has been running for over 12 years. when I clean the filter, I only rinse the media in dechlorinated water, so I would think there should be plenty of bacterial filtration. Don't have any ammonia test strips, didn't think necessary to have for an established tank, but wondering if there could be ammonia in my tap water? Only thing I can think of that would convert to nitrate so quickly. Has anyone else come across this?