Joe's right, it will cause you to go through a kajillion filters if the tank isn't cleaned. Even if you kill the stuff, it still has all the little dead remains still there that plugs things up. The best insurance is treating EVERY load of fuel that comes on, but I have to admit, I have become lazy, so I'll probably get bit somewhere down the road. Use high volume diesel stations, that reduces your chances of getting older, water laden-microbe growing diesel.
"Polishing" the fuel is a process where they remove the fuel, suck the gunk out of the tank, then return the fuel after running it through filters etc. It makes dark, ugly fuel look brand new.
Hope you get it out, and it has just started with this last fill up. Treat it right away, and possibly you could get lucky.