Diesel Fuel Biocide

Refineries add only very low levels of biocide to diesel, on the assumption it'll be used soon after it reaches the service station. But fuel often sits in vehicle or bulk storage tanks for long periods, which gives microbes every chance to grow. That's why microbial contamination is so common.

Where there's water in the tank and the temperature is right, dormant fungi, yeast and bacteria grow rapidly at the fuel and water interface at the bottom. A single microscopic cell can grow into kilograms of biomass in just 12 hours.

The first sign is usually mucus-like build-up on the fuel filters. Then come slimy, clogged filters, dark and hazy fuel, sludge in the tank, excess smoke and foul smells. Eventually it clogs the fuel lines and stops the engine. Tanks and lines may have to come out to be steam cleaned, and the fuel pump and injectors serviced: thousands of dollars, plus the downtime, and if it isn't dealt with properly, it comes back. Only a professional, concentrated diesel biocide removes or controls bacteria and fungi in a fuel system.

The 205 Microbial Field Test Kit detects fungi, yeast and bacteria before they've had a chance to develop, so you can act in time.

Boat owners are the most likely of all diesel users to have fungus and bacteria problems:

• Boats work in a wet environment, and water can seep into the tanks.
• Their fuel tanks are shaped to fit tight or awkward spaces, so they can be hard to drain, with spots where water collects undisturbed.
• The baffles that stop fuel sloshing about trap water in small pockets.
• In warm, humid climates, water in the air gets in through the breather and condenses inside the tank.

Fungus and bacteria can grow in those pockets for a long time without causing trouble, until a storm stirs them up, the colony outgrows its corner, or it dies back and the dead matter floats into the fuel. The filters start blocking with black slime, and the fungus's natural surfactants suspend water and dirt in the fuel, making it hazy.

On land, the usual prevention is to drain the water regularly, but a boat's tank may have no single point that drains every pocket. A maintenance dose of 201 at every fill stops the fungus growing; drain the water off regularly as well. If a tank is badly infested, add the kill dose and circulate the fuel so it spreads through the tank. The water and dead fungus drop to the bottom and must be drained or sucked out with a hose, or rough water will stir them up into the filters again. Keep treating for a few fills until the filters are back to normal.

Kill dose, for fuel contaminated with bacteria or fungi: 1 litre of 201 per 1,000 litres of diesel. Maintenance dose, at every fill: 1 litre per 2,000 litres.

A complete microbial clean-up

1. Pump or drain the contaminants (microbes, water and sludge) from the bottom of the fuel tank until diesel appears.
2. Dispose of the waste in an environmentally responsible way.
3. Add the kill dose of 201.
4. Fill the tank to its maximum capacity with diesel. Adding the fuel mixes the biocide through it.

Dose for the tank's total capacity, not the fuel in it. If a 2,000 litre tank holds only 1,000 litres, add enough to treat 2,000 litres.