I have never used any type of fuel stabilizer or other diesel additives. I have never had any problems. However, I only have a 12 gallon tank on my sailboat so my diesel is always fresh. On the power boat, I have two 20 gallon tanks. I run both down to about 5 gallons then fill them in the Fall. IF I had a large tank that I only used a fraction of each season I might put in an additive. As far as biocides go, I wouldn't use one unless I lived in a hot climate. Here on the coast of Maine my diesel seldom gets above 55 degrees and that only happens after a long engine run due to heated diesel going back into the tank via the return