As for the diesel algae, I work with a guy who just spent 12 years as a rep for mobil fuels.
He rekons diesel can go stale after only a week or so in the wrong conditions and he has seen personally a large underground service station tank, with what looked like carpet between the layer of diesel and water!
I can't remember the scientific name for the bug but generally you get it by filling up from a servo that has it. Even when you kill it, if it's really bad it may not break down and your fuel system will still clog with dead bug.
That's why I try to never let my tank get below 1/4 (so you don't suck the crap up) and try to always fill up at a big truck stop station as they have a higher turnover of diesel meaning less chance of bug!
as always, just my 2c
