On algae in a diesel's tank, I'm not an expert on this subject, however, over the years I have read of several causes:
1. The same fuel sitting in the tank for a long time (months).
2. Humid environments seem to encourage it.
3. Facilities that sell diesel that may not turn much of it over and/or have algae in their tanks.
The only remedy I've ever used is Biobor's product for eliminating algae.
Anyway, just what I've read on the subject-