I noticed a lot of activity on top of the water the last few days. I thought it was the BG/FHM I recently added finishing off fish food. But I noticed them today prior to feeding, I guess they are eating plankton?

Might have been fry if your bg are large enough. Mine had another late spawn and I have hundreds of tiny 1/2 inch fry everywhere.

My BG were 1-2 inch, I added them aprox 2 months ago. Went back and looked again, they are all over the top of the water and it appears they are eating something?

They could be eating tiny larva of an emerging insect hatch or zooplankton. IF it is occurring mostly during the day then it is unlikely zooplankton since they trend toward deeper water during daylight esp mid-day.

It seems to occur most in the afternoon or evenings. Today I threw some feed out and watched the less than once inch FHM attack the feed.