those look like a type of hydroid. the ones that are usually called small feather dusters (look like little fans/feathers poking out of the holes in the white tubes).
I wouldn't personally say they are bad. They usually grow on the glass, overflows and on the backs/hard to reach part of the rocks.
However, some would say they are as they may grow quickly and could potentially overrun stuff you actually want.
That's never happened to me.
When I've seen some of those in my tank, the brown ones usually, my tangs eat them!
yea, you can see some of the feathers in his picture if you look closely.
My guess is feather dusters or tube hydroids. im not 100% sure if they are diff. there maybe diff types of hydroids (I originally learned that hydroids are more like aipstasia in form, but when I looked them up more recently saw that there are feather duster types that are hydroids too...)
But I do not think either of you need to be worried. They are pretty common- the tubed feathers. I've seen some tanks with TONS of them and some with just a few, but they are easy to remove.
Yes they look like little clear/white feather dusters coming out of them. I was told they are tube worms and good. From reading I think hydroids are darked in color and not so good.
Yea they are not harmful, it is common to have a few. Most of the time they are hidden. If you have that many then you might be overdoing it on the feedings. They are filter feeders and you are growing them pretty well.