Pulling my hair out with 6.9 fuel problem

[IDIBRONCO]

That's the only thing that I can think of that could cause issues like this while sitting. It would cause instant issues. I'd think that anything else would take a while to show up.

 

[asmith]

I had my shower head disintegrate and block the pickup. It wasn't quite as bad as you are describing but it was close. It got worse and worse until finally the truck wouldnt idle. When dropped the tank and looked at the pickup it looked solid and you could barely pass air through it. and that was just plastic chunks. If yours is plastic and algae I could see it being worse.

 

[Old_F250_IDI]

I realize the OP's issue may have nothing at all to do with microbial sludge or gel growth inside the fuel tank, but could be damaged pickup tube.


Just wanted to comment:

It is not algae growth causing problems in Diesel fuel tank, it is microbial growth which turns into a gel / sludge, and can take place in untreated Diesel fuel if there is any amount of water present!

Biocide Diesel fuel additive such as Biobor JF will keep the growth from happening:

Biobor JF biocide

PS.
I am not a chemist, just a Diesel fuel user who has had this happen once long time ago, and have been adding Biobor JF in my Diesel powered equipment ever since.



Here is what I found on the Grok about the subject:

"Microbial growth in diesel fuel, often called "diesel bug", refers to the proliferation of microorganisms such as bacteria, fungi, and yeasts that contaminate and degrade the fuel. This is a common issue in stored diesel, leading to problems like sludge formation, filter clogging, corrosion, and engine issues.The primary cause is the presence of water in the fuel system, combined with the hydrocarbons in diesel serving as a food source for the microbes. Microbes are ubiquitous in the environment, but they need specific conditions to multiply significantly.Key Requirements and Causes for Microbial GrowthMicrobes require:

• Water — This is the most critical factor. Even tiny amounts (e.g., a single droplet or emulsified water) are sufficient. Water allows microbes to metabolize and reproduce. Free water settles at the bottom of tanks, creating an ideal interface layer (often called the "rag layer") where growth thrives.
  
  • Sources of water include:
    
    • Condensation inside tanks due to temperature fluctuations (e.g., day/night changes or warm/cold weather).
    • Rainwater ingress or poor sealing.
    • Absorption from humid air (adsorption/hygroscopic properties).
• Nutrients/food — Diesel hydrocarbons (and especially biodiesel components) provide the carbon and energy microbes need to grow.
• Suitable temperature — Growth accelerates in moderate to warm conditions, typically between about 10–40°C (50–104°F). Warmer temperatures speed up reproduction dramatically.
• Oxygen levels — Some microbes are aerobic (need oxygen), others anaerobic (thrive without it, like sulfate-reducing bacteria that cause corrosion).
• Time — Untreated fuel can remain stable for 6–12 months before significant contamination appears, but poor conditions accelerate this.

Why It's More Common TodayModern diesel fuels are more prone to this issue because:

• Ultra-low sulfur diesel (ULSD) and reduced aromatics make the fuel less naturally antimicrobial.
• Biodiesel blends (e.g., containing FAME — fatty acid methyl esters) are highly hygroscopic (they attract and hold water more readily) and provide extra nutrients, making microbial growth more frequent and severe.

Microbes enter the fuel after it leaves the refinery (which is initially sterile) through exposure during transport, storage, or handling. Once water is present, they can form biofilms, sludge, biomass, and corrosive by-products (e.g., acids or hydrogen sulfide).To prevent it, focus on keeping water out (e.g., good tank design, regular draining, filters, and additives) and using biocides when needed. Regular fuel testing and maintenance are key for stored diesel in tanks, vehicles, or generators."