I woke up just now in the middle of the night and flipped on a light in the house. I looked over at my tank and noticed this slender white fish (I think) darting rapidly around the tank. I had to have a closer look. I tried to snap a digital photo, but he was too fast. This was definitely not a shrimp, maybe a worm, but I have never imagined a worm swimming like this. The best I can do is describe him. It was a little less than half an inch long. The body was tapered a little to a slightly pointed tail. The head was somewhat fatter than the body and appeared very light blue in color. To add a comical note to it, he looked like a giant sperm swimming through the water - haha. It was very fast and flexible as it swam. I really don't have a clue what this could be. Hopefully nothing harmful.