It's not chemicals in the plastic or anything like that. It's the light that they allow into the fuel.
I stored a couple of blue and white drums of diesel a few years back. Even with the biocide, they started getting brown wisps in the fuel after only about a half a year. The steel drums never did that. It's got to be the light being transmitted through the plastic helping the bacteria and or fungus in the fuel to grow and reproduce.
After that, I only use metal drums for storage.
WoD
Diesel will go bad in a sealed metal tank also. Biocide is only sorta adequate.
The light getting to it sounds reasonable as a problem, but only if you store your gas tanks out in direct sunlight.
Which is not safe as plastic degrades in direct sunlight.
Anything plastic around where I live will die of sunlight in darn short order.
That includes tanks, bottles, and taillights.
One big problem we had when I was in autoparts, guys could not grasp that some plastics ain't exactly compatible with petrolatum products.
I'm sure you used the right stuff, but I never sold anything for gas that was transparent, nor did we ever get offered it by vendors, even in the gas crunch days.
Not even slightly transparent which tends to support your post.
And diesel doesn't benefit as much from stabilizer as of course, 'green things live there'.
Gasoline nowadays has additives blended into it to stop the buildup of various deposits. I've never had to do any maintenance to any of my equipment because of stale gas, thirty plus years and counting. My steel gas can's as clean inside as the day I bought it, somewhere around '75 or so.
Yup.