Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
I don't believe that's what it is and it may not be harmless.
What you describe is a bacterial fungal-type growth, which is harmless, and comes out of new wood placed in a tank, but remains attached to the wood. It can be manually removed, but will likely come back, and in time will eventually disappear. It is off-white, greyish in color.
You would not find that type of growth in the locations you see in the pics above unless you made a point of removing it from the wood, placed it in those areas, and saw to it that it stayed there.
This is completely something else, and appears to have a bluish tinge.
I could be a yeast residue that has made it's way into the tank, as the OP suspects, and if so, it is likely harmless.
deathdealer, have you tried removing it with a vacuum ?