There was a post talking about stabilzing oil, like if you start burning coal and have a tank of heating oil that may sit for months or years. Biocide was suggested to keep the oil from growing fungus or unknown salad components. Today I was buying some hydraulic fluid and saw a biocide poster on the wall. Seeing as they were selling it and I was standing right there, what better time to get some? I told the guy my intent and he said it was not what I wanted. He said biocide is for after you have fungus. He said what I wanted to stabilize the oil and prevent fungus is "Power Service Fuel Supplement". He then told me they don't sell it, but most auto parts places do. Seeing as he could have made a sale, but chose to send me someplace else, I tend to think he may be telling the truth!