Guys thank you for your opinion! I needed this.
The boat is mostly in Croatia and the fuel is good. The previous owner is never completely thin. 3 years ago, I left the tank half full over the winter, and algae grew, luckily it was a short drive so I didn't have a problem, but the filter was black! We were in Greece last year, the fuel is worse but not critically bad.
If I understood correctly, you replaced the standard prefilter with the F500?