We had two sources of "Marine" diesel here until a few weeks ago. One marina sold diesel fuel treated with Valvtec marine diesel fuel additives, it was the pricier place but the fuel had all of the additives you need like biocide, cetane booster and so forth. They suddenly locked the doors and closed up with no notice. The story is that one of the tanks had a leak but that was only one of the stories going around. My understanding is that the other fuel dock sells road diesel.

Like Steve, I get 5 gallon jugs of off-road diesel at a locak station and fill my boat at our club fuel dock when needed. I add my own stuff although I see that you can now buy Valvetec stuff in quart bottles. I have alo "heard" that off road has some different sulfur contant but once again, I have no proof to back that story up.