Microbial Bacteria in Diesel Fuel

You do not have a bug problem, you have a water problem. Bugs are everywhere but no water no life. It is that simple. Free water is the single most destructive contaminant in any fuel system and bugs are only one of it's results 
Howard L. Chesneau
Fuel Quality Services, Inc.
​Microbes Eat Fuel and Multiply 

Microbes are present everywhere, but without food and water they cannot multiply; diesel is food. When there is free water in the tank, the microbes 
have everything they need to grow, fouling fuel and damaging tanks in the process. By some estimates, a microbial colony can consume up to 1% of 
your fuel investment, while destroying the rest. 

Microbial colonies proliferate at the interface between fuel and free water 
that has settled to the bottom of the tank. This creates a “rag layer” which gives them everything they need to thrive. Warm temperatures will accelerate the growth of microbial colonies. Microbial growth can occur in any diesel fuel. Biodiesel, being made from plant and animal fats, makes especially good food for these bugs and contributes to the increased incidence of biological growth problems seen in recent years. Bugs can grow in petro diesel as well. Stagnant fuel is especially at risk. 

With time the microbial colony proliferates beyond control. This leads to acid formation, rust, corrosion and filter plugging. Fuel degrades to the point that 
it can form a slimy sludge that is unusable as fuel.
 gross stuff
This process can occur in a bulk storage tank or in a piece of equipment that is left idle for a long period of time. To the right is a classic example of what is called filter “leopard spotting”, which requires the filter to be exposed to both microbes and water. The black spots are microbial colonies. Live or dead, microbes will clog filters and damage fuel systems. It is important to eliminate bugs completely and permanently. 
Microbial colonies, sometimes incorrectly referred to as algae, are actually bacteria or fungus. Algae needs light to live and grow, there is no sunlight in a closed fuel tank so algae cannot survive. ​