I'm no expert by far, but I have similar looking white tube like things in my reef tank. From the research I've done on this forum, I've come to identify them as glass anemone. Do they have a feathery/hairy looking thing at one end? try searching glass anemone or aipasia (spelling might not be right) and look at other peoples pictures. This should help. If it is, I read that they may multiple and take over your tank. I've heard in some cases they even consume small fish. Look around the forum, I'm sure you'll find the answer. Good luck!