When there is water, diesel bacteria (sludge) or dirt (under) in or on the fuel tank, it is time to replace the boat’s engine fuel filter.
Therefore, check the filters of the fuel system regularly. E.g. annually when preparing the boat for winter. Do you see water or dirt in the inspection hole of the filter? Then it is likely that there is also water, diesel bacteria (sludge) or dirt at the bottom of the fuel tank. In that case, replace the diesel fuel filter.
Also read: Slime strings and clogged fuel filters