One step forward, two steps back....
1) Pulled out my filter, and it was definitely was pretty gnarly. It was definitely in need of a good cleaning. Got all the "Gunk" cleaned up, but diddn't see any "White stuff" though.
2) Did a 25% water change, picked up a lot of the existing white stuff from the gravel, so it's not sticking, that's good.
3) Primed and turned the filter back.
Result: All kinds of white crap blowing out of the return. Most of it was small dust like pieces like in the tank already, but much more of it and some larger pieces that were flaky looking. Really gross and right AFTER cleaning the filter?!
Best guess:
What ever this stuff was/is had accumulated in the tubing/nozzle for the filter return, there's no way that stuff was left in my filter after I cleaned it. I'm betting the filter flow rate was slowed/clogged enough that after the cleaning it boosted the flow rate and that pushed all that crud right out of the return piping.
Good news:
This doesn't seem to be bothering my fish any, so it's not harmful....so far Now that my filter is performing more efficiently, it should suck up a lot of the debris floating in the water and keep it contained to the filter.
Okay-ish news:
My tank looks like it has dandruff. Water changes will take care of the gravel, everything else I'm gonna have to take out and rinse or use an airline to suck up a little at a time which will take FOREVER.
Bad News:
I still don't know what the source of this was. Hopefully it'll be gone for good and this was a one time thing due to the poor filter flow and some sort of build up in the return.
Hoping more people will see this and maybe someone has had a similar experience and can provide more insight. Making a whole lot of assumptions