550 gallon above ground tank, I live in an agriculture area, and also have several 55 gallon plastic tanks all filled with old waste jet fuel. Current fuel inventory is about 200 gallons most of which is about 7 years old. Twice a year I pour 16 oz. of Bio Guard Diesel perseverative into the tank, label says it will treat 480 gallons so concentration is good, and then wait a few days for it to kill any fungus. After that and once a year, I get the use of my friends Alfa Laval (centrifuge) to polish the fuel, filter, and remove any water.
I know seven years is a long time for waste jet fuel, someone told me the commercial shelf life can be as high as 5 years (no cites for this claim), but with these procedures I have been lucky so far. During listeroid use, I mix a lubrication product in at 100:1. Unfortunately, the previous source for waste jet fuel has all but dried up as the aviation repair service facility found a buyer for their waste fuel products. I am interested to hear how the rest of you are doing with long term diesel storage in hot climates.