Fuel contamination

Cut the filter apart and look. Pretty easy to tell the difference. Or post a pic of what you're seeing

 

You may have combustion gasses getting into your fuel. How's it running, what truck and engine?

See what those particles do rubbed between two fingers

 

May just be the results of too much bio mix

 

I would hazard a guess to not being algae due to the defined edges of the particles, algae is a organic and will be more snotty. Without being able to see it close up and feel it it is hard to tell, Could be carbon, a coating in the lines or tank coming free or, he pissed someone off.

 

Algae in my tanks causes black slime in primary filter. Soon as it’s spun off you can see it floating on top. Looks like black silicone, different size pieces, sometimes strands of it. Look at insides of tank. If it’s solid black like a BBQ grill, might be asphaltene. More common on newer engines that run hotter than the older ones.