Toadstool, just so you know, this isn't a chat room. The people that will help you come across your thread and answer your questions. It will sometimes take some time to get a reply.
That being said, we cannot see your tank so we need a description of the tank, what you do to/with the tank, what's in the tank etc...
And most importantly, what is your question... How did it get there? How do I get rid of it? is it normal? what exactly are you asking?
There is a lot of info on these boards and we obviously love to talk about tanks and such, but you hafta be patient with us also...