Try going down to West Marine and buying some Starbrite Startron Tank cleaner. Also ValvTect claims to break down biomats. I've had great success with Startron tank cleaner.

As for the alge/fungus/bacteria debate; Your all right, the common name is HUMBUGS (hydrocarbon utilizing microorganisms)

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1999 E300DT (131,800) 154,000 Black on Black SOLD

2006 CLK 500 coupe Capri Blue on Grey (zoom,zoom)
47,000mi

04 VW TDI Passat 80,000mi
(Techno)

How to eliminate oil dependency through market-driven approaches.
“We could cut oil use in half by 2025, and by 2040, oil use could be zero,”
The Sound of Diesel Speed
Ode to MB

This stuff is a pita, at the marina last year we had to replace the tanks and fuel lines on a Trojen 36 that had the worst fungas problem I have ever seen! He would get about 2 hours out of the fuel filters before he lost a lot of power. Nothing would clean the tanks out not fuel polishing or massive amounts of Biobor.

So since the boat was 20 years old with 20 year old orignal steel tanks (cheap boat) the owner figured it would be a good time to replace them. So after all new tanks, fuel lines, and rebuilt injectors she is running like a top.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200