It might be an "Algae" problem - it's not really algae, but it's the term associated with it. You can check with pH strips.
From one source -.
4. Your fuel pH is lower than it should be. Algae in diesel fuel produce acids that gradually skew the fuel's pH towards an acidic environment. A pH of 7.0 is neutral, so adding acid to the fuel will decrease the pH number. A fuel pH of less than 5.8 indicates a serious problem and is strong evidence that there's a microbe problem going on in the tank. Finding this out requires a pH meter, of course, so if you have one, it's another bullet in the arsenal of evidence that you can collect to determine if you've got a diesel fuel algae problem.
They may have picked up a bad load of fuel.