I'm counting environmental samples stained with DAPI and counting the bacterial to algal ratios by counting the stained bacteria vs the autofluorescence of the chloroplasts. I'm using a Zeiss epifluorescent microscope loaded with filter sets 38 ( BP: 470/40, FT: 495, BP: 525/50) filter 43 (BP: 545/25, FT: 570, BP: 605/70), and filter set 49 (G: 365, FT: 395, BP: 445/50). The DAPI is staining and visualized with filter 49. When excited with blue light, I can clearly see small cyanobacteria fluorescing a light green and larger microalgae chloroplasts fluorescing red in filter 38 (BP: 470/40, FT: 495, BP: 525/50) but I can also see both of these types of cells fluorescing red under green light with the filter 43 (BP: 545/25, FT: 570, BP: 605/70). 

I have 3 questions:

1) Is this red fluorescence from the green light excitation an artifact cause by Chl a, Chl b, and/or other phycobiliproteins?

2) Could it be some other autofluorescent biomolecule?

3) Can you briefly describe the 3 number for each filter? I understand that BP is band pass and only allows light within the described range through, but does the order matter and what is FT and G?