Question for you ABYC guys about prop corrosion
 

So last year we got a new to us express cruiser with bravo 3x drives and stainless props. I am having an issue with buildup on my props. I clean , polish and seal and after 2 days or 2 nights on the water, the props have a thick chalky buildup and are no longer shiny. The boat has an Kohler 5e genset and we use the genset tied up to other boat all weekend. The boat also has an electronic galvanic isolater but Im pretty shure that only protects when plugged into shore power. I have made sure the drives are connected to the 12v ground system and I have also even tried adding anodes to the end of the prop shaft. The lake we are always in is fresh water but does have a high mineral content.
I have been ready about and starting to think that maybe for some reason the neutral and ground on the genset are not grounded or maybe the floating voltage could be coming from the boat I'm always tied up next to ? Also wanted to note that our previous boat had a similar issue and it did not have a genset but we did plug shore power into the same boat we tie up to currently so again, maybe something on that boat causing the issue?

I would greatly appreciate if one of you could give me some things to test to help eliminate this issue.