Mine came out of nowhere as well. When I noticed them I hadn't added anything in a long time. A week ago I started cycling some old dry rock that I had removed from the tank a year ago and noticed some of the dried tubes on it. I hadn't noticed them before but there they were; I've had them in my tank for a long time. They've never been an issue and I kalk them when I feel like it but it's not something I worry too much about.
