whatisthis?

Hi there, These started as little nubs on my algae scrubber and now have grown little feathers like feather dusters. They look like sponges with tiny feather worms inside. Are they pests?? They only seem to be on the algae scrubber so I can remove easily if they are.

Can't figure out what these are. They're very small. The parts on the string like structure are the size of a larger copipod. They don't move except the large pieces move with the current. They don't pulse or anything that I can tell. There are multiple on the walls of my tank. Some are just a...

Hi, Im a new reefer and was gifted some corals. I've asked my local reef store and they think it might be some type of mushroom?? I'm not sure where to put it or how to take care of it because I dont know what it is... if anyone has any idea, any tips would be greatly appreciated!