This dual-phased (effective in both diesel fuel and water) biocide kills microbes in fuel, including bacteria and fungus. Use this product to rid your fuel system of microbial contamination. Bio kleen diesel fuel biocide kills microbes in diesel fuel. The dramatically reduced sulfur content in today's cleaner burning fuels has created ideal opportunities for microbes to grow in fuel tanks. The first indication of microbial contamination is mucous-like accumulations on fuel-filters and increased requirements for fuel-filter replacement. The only way to get rid of microbial contamination is to kill the microbes with a biocide.