I got a feather duster by mail. On placement into the tank, the worm like thing itself emerged partially. I pushed the transparent part into the sand bed. Next day, the tube opening was in a rock hole. I left it there. Next day I took it out, and after waiting a week, no dutser emrged. I looked at it more closely today, and the whole thing appears hollow. I have another feather duster that is perfectly content. What happened?