I have to agree with Layback on the bacteriological infection. Probably fueled at a station that had the bacteria. The antibacterial suggested should do the trick but... you might have to change the filters a few times till things clear up.
To avoid the problem, as already suggested, go to high volume fuel stations. I always go to truck stops; they almost always have the best fuel.
As for filtering and reusing the old fuel... you can't really infect an already infected system. If you want to use the fuel, you could let it sediment then pour the more or less clear fuel thru the coffee filter I guess.
I would NOT take fuel from a car with a bacteriological/algal infection and put it in a car that doesn't have such an infection. Filtered or no you are only asking for trouble.

Finally, does the bacteria/algae whatever develop over years... I suppose it does like any life form. May be some use for it. Maybe it's a derivative of the bacteria used to clean up oil spills?

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Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)