Interesting Discovery After Winter Layup

[Fishtales]

Took the shrink wrap off and found a purple color stain across much of the euro transom. I've never seen anything like it. I might get a bit of mold here and there, sometimes even on the rear fiberglass covers on the fishbox. I use some Zep mold and mildew and it usually takes care of it. This purple stuff wasn't coming off with any of my usual cleaners or mold stuff.
I tried hull cleaner which didn't do anything. Finally tried On/Off and like magic, it removed the fungus/stain or what ever it was.

Anybody ever have something like this? I'm curious what it could have been.

 

[seasick]

On and Off is effective on algae and rust stains. Mold and mildew cleaners are bleach based not acid based. Assuming the stain wasn't rust ( purple is usually not the color of rust), the stain may have been algae growth.
On and Off can damage metal including galvanized trailers so make sure you rinse really well and avoid spraying it directly on metal parts and trim

 

[Fishtales]

I was careful and it was on stands. It all ran out the aft. It had to be some sort of growth, but it is gone now...