There are many believers in additives. Perhaps that was a water free tank that needed no additive. The fuel makers say that they put the right stuff in. If your fuel has no problem, leave it alone. If it does have a problem, get it out of there and put in good fuel.
Good fuel is the second most important thing in diesel maintenance, after the lube oil.
I know that too much of the wrong additive can cause problems. There is word that some additives react with other additives. I personally would rather play safe and keep my tank clean. It seems foolhardy to me that many owners gamble with a ten-dollar jug of additive to try to resurrect fifty dollars worth of fuel when the heart of a ten thousand dollar engine is at stake. This week Marine Diesel Direct expanded it online reference materials with the addition of an index of Yanmar starters and information about Yanmar's rebuilt alternator program.