Standard grades of diesel are clear and usually light yellow. The smallest discoloration can be a sign of bacteria, mould or yeasts. If your tank is contaminated with microbial pests they will form bio-sludge. This is a slimy, brownish mass which may float on the fuel or may form deposits at the tank walls and results in filter blocking and corrosion. Eventually sudden engine failure will occur. Even filter changing often does not solve the problem; the microbes produce new sludge in a few hours and block the filter again. In the course of time the bio-sludge sticks on the surfaces, it gets more and more difficult to remove it. Often a costly professional tank cleaning becomes necessary. To avoid this trouble it is advisable to test the tank with mikrocount® fuel regularly. If microbes are detected, treat the fuel with grotamar® 82 according to the severity of the contamination.