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How to Get Rid of and Prevent Algae in Diesel Fuel


All diesel users should be aware of the possibility of algae growth in their fuel tanks. This growing problem can be solved and prevented by following a few simple steps.

Diesel algae can be prevented by maintaining water levels in the tank. The use of a water controller will help regulate water buildup in diesel fuel. If algae begins to grow in the fuel tank, drain excess water and treat the fuel with a regulated biocide.

Algae in your fuel tank is not a problem that should be ignored. Once algae has been discovered in your fuel tank, follow the steps below to remove the problem and prevent it from occurring again!

What is Diesel Algae?

Before we discuss how to remove and prevent diesel algae, it is important to discuss what the substance growing in your tank ACTUALLY is.

Diesel “algae” is in fact, not algae at all. Although commonly referred to as such, the substance growing in your fuel tank is just bacteria and fungus. While algae and the substance in your tank are both a form of microbes, there is a key difference between the two.

Algae is a plant, bacteria is not. Unlike bacteria, algae require light to survive. Because a fuel tank does not let light in, actual algae cannot survive there. Although it’s not actually a type of algae growing in your diesel fuel, we will continue to use the term “diesel algae” throughout this post to reduce confusion.

Over time, diesel begins to separate from the water it is mixed with. This water creates the perfect environment for microbes to exist. Additionally, if you are in an area with higher temperatures and levels of humidity you are more likely to find diesel algae in your fuel tank.

Now that we know more about what diesel algae are, let us discuss why they should not be inside your fuel tank. The microbes and bacteria that makeup diesel algae feed on the fuel’s hydrocarbons and then release a by-product into the tank.

This process weakens the fuel’s stability and fills the tank with a layer of dark sludge. Running this fuel (and the sludge inside of it) will clog the engine filter. This will not only have a significant impact on your engine but on your wallet as well.

As well as harming the fuel, diesel algae cause harm to the tank itself. The by-products of the bacteria living in your tank are acidic and can lead to corrosion of the tank. If ignored, you will find yourself needing to replace the entire fuel system.

While diesel algae can be extremely damaging, it is also highly preventable and treatable. Learn how to remove diesel algae from your fuel tank in the next section!

How to Remove Diesel Algae

Diesel algae is not a problem that should not be ignored. Follow the steps outlined below to prevent any further damage to your vehicle.

Start by draining the excess water from the fuel tank. You want to ensure there is no water left inside the tank that will allow bacteria to remain inside. This will lead to repeated corruption.

Once all the water has been removed from the tank, add a biocide to the fuel. This biocide will kill any of the microbes that are clinging to the tank and the fuel. Additionally, the use of a biocide in your diesel fuel will make it harder for algae to return to the tank.

Be sure to use a proper amount of biocide. If you only have 1/3 of a tank of fuel, still add enough treatment for a full tank. As mentioned above, some bacteria will cling to the tank’s walls above the fuel line. If there is only enough biocide in the fuel for 1/3 of the tank, the biocide will be too “watered down” to kill these lingering bacteria when you refuel.

Using enough treatment for a full tank ensures that the mixture will still be strong enough to rid the tank of diesel algae even after refueling. You should not pour the biocide on top of the fuel. While it will help clear some diesel algae from the tank, it will miss the main cluster.

Because water is denser than diesel fuel, it settles at the bottom of the tank as it separates from the fuel. Since the fuel sits on top of the water, pouring the biocide on top of it and leaving it will not allow it to reach the contaminated water at the bottom of the tank.

Ensure that biocide is thoroughly mixed with the infected fuel by injecting it into the fuel line. However, if you do not have the equipment to inject it into the fuel line, there is another solution you can use. Simply, add the biocide and then circulate the fuel. This will still be more effective than simply pouring the biocide in and leaving it to sit.

After running biocide through your fuel, you will need to change the fuel filter as it will have collected the dead microbes. Continue changing the filter as needed until the problem is resolved.

If there is already a layer of sludge inside your fuel tank, draining the tank and treating the bacteria will not be enough to clean this layer out. You will need to use a mobile fuel polishing system to remove the sludge from the tank (source).

This system removes the fuel out of the tank and filters out the dark sludge. While this method does remove excess water and existing bacteria from the fuel tank, it should not be used for the long-term prevention of diesel algae growth. (Learn more about other methods to use instead in the section “How to Prevent Diesel Algae” below.)

Finding the Right Biocide

While purchasing biocide for your diesel algae may sound as simple as taking a trip to the auto store, it is a bit more complicated. There are hundreds of products claiming to rid your tank of bacteria and algae; however, not all of them work.

Biocides must be registered with both the Environmental Protection Agency (EPA) as well as the state they are being sold in. If a product lists that it is approved by both, this is a good sign that it is a quality product. However, if the product is only registered with one or has no registrations, it may not meet industry and safety standards for effective use.

As well as showing proper registration, the label of biocide should include a significant list of safety warnings. Because biocide is such a toxic chemical, users must be notified of the proper usage and potential harm. The biocide can kill any living thing it comes in contact with. In other words, it has the potential to harm more than just the diesel algae in your fuel.

If the product you are looking to purchase does not include a long list of safety warnings and instructions for proper usage, look elsewhere. Either the product is not effective enough to need safety warnings or it is violating the law.

You should only purchase biocides that meet the legal requirements. Any product that does not meet these standards should not be purchased or used in your fuel tank.

Although biocides are usually an effective choice for removing diesel algae, they should be used with some reservation. If the diesel algae in your tank are frequently exposed to biocides it will create a biocide-resistant strain of microbes. This will make your problem virtually impossible to resolve.

Do not simply rely on biocides to rid diesel algae from your fuel. Rather, you should use preventative measures to avoid using biocides in the first place. Learn how to prevent diesel algae growth in your fuel in the next section!

How to Prevent Diesel Algae

Preventing algae growth in diesel fuel can be accomplished by minimizing water in the fuel tank and by applying an appropriate fuel additive.

Diesel algae growth in your fuel tank can be easily avoided by following some simple preventative measures. We spoke with an experienced semi-truck driver to learn what he did to prevent algae growth in his fuel tanks.

Before we discuss what method that Neal, a semi-truck driver of nearly 20 years uses, let us look at some of the many diesel algae prevention options you can use in your fuel tank. Because diesel algae require water to survive, you should frequently be checking the water levels in your fuel tank. Water levels should never reach more than half an inch. The more water there is in your fuel tank, the more likely you are to experience diesel algae.

Check the water levels in your fuel tank with the tank stick. This will require the use of water-detecting paste. If you do not want to manually check your tank’s water levels, some automatic sensors check the levels for you. Add one of these sensors to your fuel tank to stay on top of water management.

If there is too much water inside your fuel tank, immediately drain it out. You can then use a chemical treatment to dry out the tank. Leaving water to accumulate inside of the tank will absolutely lead to algae growth. This is especially true if the tank has already been exposed to algae growth before.

Another preventative measure you can take is to ensure that the tank has not had diesel algae in it before. If you are purchasing a new vehicle or storage tank, check the tank for diesel algae or signs of past exposure. If there are bacteria found currently inside the tank treat the fuel with a biocide. If the tank does not currently have diesel algae but it has in the past, you will need to pay closer attention to water levels to ensure the dormant bacteria is not able to reactivate, contaminating the fuel.

Managing water levels in your fuel tank can be done with more than just draining excess water every so often. Adding a water controller to your fuel tank will prevent the fuel and the water from separating in the first place.

Water controllers pull the water back into the fuel. If the water does not separate from the fuel, then the chances of diesel algae growing in the tank are greatly reduced.

This is the method that Neal swears by. In all his years of driving semi, he has yet to experience diesel algae. He uses Howe’s Diesel Treatment (link to Amazon) in his fuel tank.

This treatment not only prevents the fuel from gelling in colder temperatures, but it removes excess water from the tank. Without water in the tank, the chances of algae growth drop to zero.

Another preventative measure would be to add “diesel algae preventatives” to the fuel tank. While these products were once effective, there is not much evidence of these working effectively with the current mix of diesel fuel. So, what changed? Why do algae preventatives no longer work? Find out in the section below!

Diesel Algae: A Growing Problem

Issues with algae growth in diesel fuels is increasing.

A few decades ago, diesel algae was a rare occurrence and could be prevented with the use of algae preventatives. Today, diesel algae is becoming a more frequent problem and preventative measures that once worked are becoming obsolete.

What changed to cause this? The simple answer is the fuel. Previous diesel mixtures contained higher levels of sulfur. The sulfur present in the fuel made it difficult for bacteria to inhabit fuel tanks. However, this fuel is being phased out and Ultra-Low Sulfur Diesel (ULSD) fuel is taking its place.

Ultra-Low Sulfur Diesel fuel is becoming more popular because it is more environmentally friendly. Sulfur is removed from the fuel at the refinery and is therefore not released into the air as the fuel is used. This reduces the likelihood of issues such as acid rain occurring.

Unfortunately, this low-sulfur fuel makes it easier for microbes and bacteria to grow inside fuel tanks.

Unless you are still using the older diesel fuel, chances are you will have an encounter with diesel algae at least once. Follow the steps described above to remove and prevent diesel algae. Hopefully, if these steps are followed properly, it will only be an issue you have to deal with once.

Related Reading:

Why A Diesel Engine Loses Power After It Gets Hot

Teddy Henderson

Teddy is always fiddling with small engines, picking up thrown-out string trimmers or tearing apart dirt bikes. He shares what he learns along the way. Hopefully, you'll have less headaches than he has had by learning from his mistakes.

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