Hi spiketooth. I noticed something very similar in my tank, except mine are inside the tank. It was a guppy tank until very recently. I know have balloon mollies in there. I noticed them a while back, when the guppies where in there. One of my b.mollies recently gave birth and when I was searching for fry, I noticed them again. They seem to hang around my internal filter. I have also noticed them free swimming. I would be very interested to find out what they are and are they harmful??. As you know, being so small, they are impossible to photograph...