Interesting about the feather dusters making their tubes over time. I have had our tank (46 g) for about 3 months and it is doing really well. Recently I had started to notice this very very small white tubes (about 1/2" to 3/4" long) stuck in about 4 or so places on my live rock. Had no idea what they could be until my 12 year old noticed the feathers sticking out of them. They stick out only about a 1/4". Were these things hiding all this time? We started out by getting the tank complete from someone, and about a month after we started, we added more live rock. Actually, I am assuming that these ARE feather dusters, but they are SO small, maybe they could be something else??? They are really even too small and in too hard of places for me to take a picture of them.
I also have these tiny, hard, white sticks(?) that have started to show up in various places on my live rock too. I imagine that they could have always been there, but the algae is changing and now they might be showing up? They arent growing or anything, so they might be nothing.
Just don't touch them, let them stay in the place they are now.