I found another one, this time I tried to get a little bit closer.
20131221-DSLR_IMG_0016-Edit.jpg by pwnell, on Flickr
Tropical aquarium - Centropyxis amoeba test, 40x, DIC, HF B+A
20131221-DSLR_IMG_0056-Edit.jpg by pwnell, on Flickr
Tropical aquarium Centropyxis amoeba test, 60x, DIC
20131221-DSLR_IMG_0162.jpg by pwnell, on Flickr
Tropical aquarium - Centropyxis amoeba test, 60x, FLUO-C6
It is clear from the last image that the diatoms used in the test are all dead - the diatoms / cyanobacteria / algae fluorescing I presume are not part of the test but rather just hitching a ride.
Images made through a microscope. All subject types.