I guess I do need some pics of what a good bacteria colony looks like compared to bad "mulm". Sounds like it is important enough to know the difference.

When the "mulm" is cleaned off the moving bacteria filters, what becomes of it? Does it settle and eventually gets flushed? Or something else?

Thanks for helping to clarify this stuff. I have heard/read different things about "this" but nobody ever explained it really well, leaving it a bit ambiguous, probably because they didn't know themselves.