Fuel tank algae

My coworker has a farm as a side job. He started having algae issues with his tractors just out of the blue summer of 2018. He found this summer that the local COOP had started delivering Bio-diesel as their standard farm fuel because it was cheaper. He had to request the standard diesel if he wanted it.

So what’s the difference? Standard petroleum fuel- the bacteria that created it supposedly died off millions of years ago.
Bio-fuel- the bacteria that created it supposedly died of last week......

Moral of the story- know your fuel suppliers.