This stuff is on one of my decorations nearest the filter. I am a little ways into a fishless cycle. I've brought my tank up to 2ppm ammonia and in about 6 days it was down to .25 ppm so I brought it back up to 2ppm anf again in like 6 days it was down again. So I brought it up to around 3 or 4 ppm and it's been stuck there for approximately 5 days. I also have not seen any nitrites or nitrates yet. I don't know what's going on or what this stuff is on decoration just noticed it today.