Cleaning Wood Spreader

[Me-and-Boo]

With my mast on stands I have a good opportunity to properly strip down and revarnish the wood spreaders. One of them has a green growth on the wood. I have hit it with hydrogen peroxide, bleach, dish soap and light sanding. To no avail.

It is not paint. It is the same stuff that was on the deck that I power washed off and then keep at bay with deck cleaner.

What can I use to clean the wood? Or is it just varnish over the top of the stuff and pay no attention to the color.