I happen to unscrew the cap on one of my bathroom taps, which is caked in scale. On top, I found this fetching pile of bluish coarse powder loosely sitting on top of the plastic mesh. Is this supposed to be there? I would assume this is debris that should be cleared but it looks like no debris I've seen. It's not some all-natural filtration thing, is it? Seems unlikely, but I thought I'd check.