How Can You Tell if There is Algae in Your Diesel Fuel Tank?

How can something grow in diesel fuel?  Well, it doesn't technically grow in the fuel, it grows in the water - diesel fuel interface. Water is the food it needs to grow. Water can form in your fuel tank through condensation. If it gets bad enough it can prematurely plug up your filters. Old diesel that has sat idle for long periods of time are more susceptible to this problem. The first signs will be small black specks in your clear pre-filters. To find out how bad it is, you have to inspect inside your fuel tank. That can best be done by removing the fuel sending unit.  If it is all black like you see in this picture you probably have algae growth in your tank.