Plugged filter and visible bio sludge in the tank are often the first signs of a microbial contamination, but these can also be caused by other contamination without the influence of microbes.
If a thick layer of bio sludge is visible in the fuel tank or bio films are sticking to the wall, then it is usually too late to sanitize the tank with a shock treatment. The tank cleaning must be cleaned thoroughly! The persistent bio film need to be removed mechanically to prevent a recontamination. After an in-depth tank and pipeline cleaning the contaminated diesel fuel should be treated with a shock dose of grotamar® 82.
Please bear in mind that after the addition of grotamar® 82 dead microbes can plug the filter and an additional filter change may soon be required. The dead microbes will not be dissolved by grotamar® 82 because it does not contain acid. Acid would attack the material in the tank system.