on a serious note I would guess it is some king of bacterial bloom? a photo of it would help if at all possible. I've heard about this but not seen it!
you'll be amazed at the results you get when you search the forum for 'white fluff' it appears to be very common and nothing to worry about, try it! here's an extract I found:
In your case gavy, what you're seeing is sure to be bacterial biofilm. Since bacteria of many types will colonize all the interior surfaces of a tank (once chlorine/chloramine is removed from the water it becomes their perfect home environment of course confused.gif ) you will see these telltale signs of their colonies. They are completely harmless and actually a sign of a healthy tank getting started up. They will eventually just go away as the tank matures. There's also nothing wrong with cleaning them, but if you're doing a fishless cycle the preference is to just leave all this stuff in the name of not disturbing any of the overall bacterial startup.
Virtually all of the bacterial colonization we care about is in the filter where there is a nice flow of fresh oxygen and ammonia that encourages the bacteria to divide and grow. But at the very start of fishless cycling, there are very few of the two species you're hoping to encourage and so its wise to just let them be left alone to grow whereever they happen to stick and begin a little colony. It could very well be that a few that started out in the tank will divide and send off floaters that will get lodged in the filter and help those spots get initiated.
Anyway, just mentioning this for gavy. In fillthehole's case, we don't really know what percentage of the white fluff getting shot out of the Fluval is really pieces of biofilm or just other particles that haven't been mechanically trapped by the filter. Certainly an interesting set of info there from strangeworld.. feel like my Fluval education has been enhanced, since I've never had one myself.
~~waterdrop~~