[tubman]

I wouldn't suspect the fuel additive as much as the tank itself (and the associated lines). Unless you are absolutely sure the rest of the system is scrupulously clean, there is a very good chance it has contaminants in it. Even if the tank has been cleaned and coated in the past, there is still a good chance that the coating used has deteriorated to the point where it could be causing the problem. A quick journey through this forum will yield many anecdotes where people have removed and cleaned and treated the original tank and still had a problem. Most end up replacing the tank in order to permanently solve the problem.