u/MelopsitaccusUndu

Can anyone... Identify this... Whatever this is? The fluffy thing that's moving in the flow. My tank is fresh water, years old, I use German hmf filtration (flat sponge filter for edges). I didn't put anything new in it. When some pieces fall off this fluffy thing, the guppies eat it. It's dark in that corner, fully dark. No sunlight. I thought it was some kind of stuck marimo moss pieces because I fully removed the marimo moss balls. But algae need at least a bit of light.

Is that... Just dirt that grows super slow? Bacteria? Can they grow in fluffy pieces? Or is that a super algae that can grow in darkness? I'm at a loss.

Is this sunbleached with a perfect way or is that really missing ink? I am super unsure. Usually bleaching leaves only blue, but the fire symbol is still fully there