I would start at the tank filter and work from there, including the lift. If you had a "bit of an algae problem" that tank filter will be pretty clogged.
You can even get algae clogging the lines, just like plaque in our arteries from eating all those fried foods so you can have your fuel.

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1987 350SDL Parts Car
1987 350SDL #2 Sons Car
1991 350SD My Car-RIP 9/7/09
1992 300SD Her Car
1995 E300 Spare Car-RIP 4/23/09
1992 S320 My Car - Soon to be diesel
1990 W250 4x4 Cummins #1 Son's Truck
1993 D350 Cummins My Truck
1999 3500 Cummins Just Another Truck
1987 Executive Cat 3208 Family Wagon

"Growing up is a choice. Growing old is a privilege"