Are these feather dusters and would you scrap them off or leave them?

[AWarnick]

These are growing on the underside of my return flex tube. They look like very small feather dusters but wanted to check and see if I should leave them be or clean them off?

Any advice appreciated.

 

[jcook54]

I like them and only clean them off if they're potentially going to bock something. I've got them growing in my overflow compartment and on the underside of some rocks. When they start growing on my return stand pipe, I scrape them off because they can restrict flow if they get enough of them together. If you see them just doing their thing where they can't lead to a blockage or flow restriction, they're harmless filter feeders.