I am in the process of doing a fishless cycle in the new tank and I just changed some of the water. Looking in the tank afterwards we noticed what looked like a fine film, like a very fine gossamer, attached to the side of the tank and floating in the current. Looking in the top we could see the same sort of substance along all the silicone seals. It's not a thick sludge, and it seems colourless or translucent white rather than green so I don't think it's algae (there's no sign of algae anywhere else in the tank either). Is this beneficial bacteria growing to help the fish be happy, or might it be a Lethal Killer Substance[sup]TM[/sup] that I need to deal with?