Depends on how much fuel you buy at a time, where you live etc. I buy 60 gallons in two 30 gallon barrels a year in the fall and treat it with anti-gel and injector cleaner. For my Motor Home I don't use anything. For my Pick-up I use the Anti-Gel in the winter and injector cleaner as the Chevy LB7 is known to have injector problems. The 12 valve Cummins in the motor home is only run in the nice weather and has no known injector issues. So if you buy small quantities of fuel, I would treat it only for the season with a good anti-gel if you live in a cold climate. Clean fuel is more important for almost any season. My fuel pump on the 30 gallon drum has a fuel/water filter and is sealed when the pump is not being used, I only open the vent when pumping fuel. I installed the diesel fuel filter system after I had issues early on and a valve was installed after I found water being drawn into the barrels when left open to the atmosphere.