I am having a problem with Garapa turning black. It gets small black spots that seem to permeate the wood, then blend together. It happens when the wood gets wet, and wet doesn't happen often. We have cleaned decks, both with new wood and redoing wood that was already down with Messmer's Phosphate cleaner, Oxy clean and bleach at different times. We coat with Messmers UV Plus for SoCal forumla that is tinted.

I've redone these decks twice and the problem keeps recurring, mostly where there is sun and moisture (dew overnight even is a catalyst.) Shade and/or undercover this does not occur.

The supplier and other experts say to clean with bleach, coat with the protectorant and all should be good. But it keeps coming back. I live in the hills abutting the Santa Monica Mountains, so there are lots of trees, pollen, etc. The supplier ways once cleaned, and the mold killed with bleach, and then sealed, this should not happen. Very frustrating.

Wondering whether this is mold or something else? And if it is something that can be prevented?