I'd please

[Aussieiniowa]

I found a few of these on the underside of some live rock and on the back of my uv filter not sure what it is

 

[AquaFrenzy]

think they are tube worms, the same you find in wet/dry systems and inside overflows, from what I have read they are harmless and feed on excessive nutrients in the water.

 

[Aussieiniowa]

Thanks I do have a few baby feather worms

 

[cloak]

Spirorbid worms. (harmless)