This means you definately have a fugus problem , algae cannot grow in the dark tank .

Don't panic , just continue the routine maitenance procedures and get some Startron , it's a liquid you add 3 Oz. to each full tank of fuel and it'll kill and disolve the resultant crud so it passes through the engne and is burned , the alternative is removing the fuel tank and having it cleaned , mucho labor and some $ , Startron (boat stores) will allow you to drive it clean ~ really it will .

Enjoy your new (old) Mercedes ! she sounds like a pip .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better