I have just spotted some more odd tank life! It looks a bit like a really thin, elongated blood worm, although it is white. I saw it moving on the glass like a leech, it grabbed onto the glass then pulled the rest of its body along. Then it jumped off the glass and spiralled down onto the ground where it hid in the plant's, I couldn't get a picture of it, and I can only see 1, what is this?