Heating Oil Tank Additives?

I'd like to take advantage of the DIP in HHO to fill my tank which hasn't been filled since spring of 2010 and is currently just under 1/2. I put Biocide treatment in it probably almost 4 years ago and have been pumping out of it over the last few months for my tractor (20- 30 gal total). Tractor has been running it w/out issue, I do notice a bit more black smoke compared to the taxed diesel, but this is probably due to the sulfur content. My tank I am assuming is new with the house in 96, but all in all seems to be in reasonable shape.

Am I inviting trouble simply topping it off w/out using more of the old stuff up? My neighbor says I should add a gallon of isopropyl alcohol to prevent rust. Thanks

Whatever you do don't add any alchohol. If you're not going to use the oil, keep the tank full because you'll have significantly less water from condensation in the oil over time. Add a biocide periodically and I like powerservice white bottle to keep the fuel treated otherwise. No need to use up what's in there, but it doesn't hurt to drain a gallon or two off the bottom from time to time (once or twice/year); if your tank is properly pitched and your supply comes off the bottom, any water should collect there.

I add Pri-D to my tank along with the biocides you mentioned. Another thing that makes me at least feel better is polishing the full by pumping it through a filter and back into the tank.

My filter absorbs water as well as filters so I just run the pump for an hour or so once in a while with the hose stuck into the tank fill hole. Some use special multi filters for this set up on a cart, but I just use my regular good quality filter.

I would likely polish and then retreat the fuel and then top it up.

SD