Here are some closeups of exactly how this layer looks like. It is clear to me that there are multiple different species go bacteria just going on morphological differences. And naturally, as many organisms feed on microbes, this is the ideal place for a nice buffet. Just sad the bacteria seems to be winning...

20140128-DSLR_IMG_0019.jpg by pwnell, on Flickr
Tropical aquarium surface film - bacteria, 60x, DIC, HF B

20140128-DSLR_IMG_0019.jpg by pwnell, on Flickr
Tropical aquarium surface film - bacteria, 60x, DIC, HF B (100% crop)

20140128-DSLR_IMG_0052.jpg by pwnell, on Flickr
Tropical aquarium surface film - bacteria, 60x, DIC

20140128-DSLR_IMG_0050.jpg by pwnell, on Flickr
Tropical aquarium surface film - bacteria and testate amoebas, 60x, DIC

20140128-DSLR_IMG_0066.jpg by pwnell, on Flickr
Tropical aquarium surface film - bacteria and diatoms, 60x, DIC
As Steve Jobs was famous for saying - but wait, there's more:

20140128-DSLR_IMG_0069.jpg by pwnell, on Flickr
Tropical aquarium surface film - bacteria and diatoms, 60x, DIC