What is this and is it good or bad? The fanlike thing on the bottom left. I haven’t seen the barnacles active and they are a bit bigger than the fan thing.
Thanks!
There are spirobid worms on base- Harmless but multiply. Can be toothbrush off and siphoned.
Often referred to a feather dusters, these are actually tube worms which use the fan to capture foof. Directing flow towards them, not at them will cause them to starve