Here are some pics of my pond scum this morning. Mike - do these look like your earlier pond conditions?
It seems like it's getting more concentrated/intense and there are a few things going on...
1.) Bubbles that do not pop quickly. High surface tension along with a surface film, maybe proteins and algae bloom? These bubbles area gone by the afternoon.
2.) Look closely and you can see veins of brown and green through out the pond's upper water column. This is hard to see in the potos, but there are definitely below-surface color patterns. Different types of PA blooms or stages of blooms?
3.) A surface film of green where the diffusers have pushed it away from the center of the pond. A different bloom all together?
I can't help but wonder how running the aerators only at night affects the bloom cycles. The water gets thoroughly churned at night, mixing the previous day's algae growth to a consistent density throughout the water column. Then the lack of mixing during the daytime may be killing off the algae that can't get light because its towards the bottom of the water column. This may explain the green and brown veins and the dead PA may be floating to the top causing the floaty scum. I don't know, but it's the best mumbo-jumbo I got!