Diesel bug is very common in boats where the water vapour in stainless steel tanks helps it to breed.
The solution is to keep tanks brimmed (expensive when you have two 320 litre tanks) or as previously mentioned, use a biocide treatment in your fuel.
I’ve used various different ones on our boat but can’t say if any better than the others as we have never suffered the problem.
That may well be down to treating our tanks or the fact that our boat is used regularly and not laid up over winter.
Certainly worth trying some in the car
