Planted Tank Guru
Join Date: Jul 2008
Location: East Lansing, MI, USA
The NutraFin Cycle jump started your bacterial cycle, as it should have.
As others said, it's protein scum. In a marine tank this is what a protein skimmer takes out. In a freshwater tank, surface agitation will usually keep this down, after the initial bloom. Scoop it out, or catch in the cup from underneath. IF it continues to build, Then you'll need to look at contamination from something. Perhaps the small bit of lubricant that allows the tank builders to remove glass off the pile.
I like to wash tanks, particularly brand new ones, with a paste of salt and a bit of water. The salt scrubs without scratching and sanitizes.