I have spotted a few tiny white snails on the glass, is there any such thing as a bad snail for a reef tank. They are very small and I cannot get a decent picture because of their size. I have also seen a very small white worm on the glass bout 2-3mm in length moving slowly. I have checked online and the Hitchhiker sticky posted by Little Fish (Thanx by the way it was a great read) and have not spotted it. I am of the belief that when in doubt pull it out. I have not seen the worm since but when I do I will try to pull it out but I will try to get a pic of the worm if I see again.