White film on black sand?

Thought I would share this picture of my sand to see if anyone might have any clue what this might be. It's a white film, which is visible from the picture. It seems to be around mostly where green hair algae was in my sand, but the green hair algae seems to be disappearing in the sand bed since adding my Yellow Tang and Protein Skimmer.. Any clues? Or is this just associated with death of green hair algae, likely brought on by my protein skimmer stealing nutrients?











Also, thought I would share my nice Green and Purple growth in my tank. Green is moreso on the back glass, no purple there yet, but definitely getting it on my LR.