With the onset of cold weather you should be sure you fill up with winterized fuel to keep it flowing freely and not gel. You may wish to add a fungicide to prevent algae build up in your tank. Beyond that some people put in additives but many do not.
I ONLY use anti gel additives in the winter, and after looking at Project Farms test I concluded I'll continue using Howes for anti gel additive, it is pretty a reasonable product price wise.