Black Spots on Deck Boards

[Black Spots on Deck Boards]

Thank you both for your responses.

Is their an off-the-shelf product that containes Sodium Hypochlorite, soap surfactant, and Dihydrogen Monoxide with your suggested ratio?

[Black Spots on Deck Boards]

Hello,

I had # 1 clear kiln & dry pressure treated yellow pine decking boards installed last July with ring shank galvanized nails.

I have not been able to apply a stain/sealer yet (14 months later)

Now black spots are appearing on most of the boards.
It seems as if small cracks are developing and from those comes the black spots.

Tried Oxalic Acid based cleaner but made no difference - i don't think it is Iron Oxide Stains
I was going to apply a light semi transparent stain but now rethinking a darker maybe solid stain to hide the spots.
Any ideas what these spots are and if they will cause a problem after staining?
I have attached pictures.
Thanks for any help,

-Tim

[Cleaner left white residue on deck]

Hello,

New PT deck built in April.

Last week applied Cabot Problem Solver Wood Cleaner and pressure washed.

Now most of deck has left over white residue in the either "fuzzies" created by cleaner and/or in streaks created by too much power on the pressure washer.

I assume I did not keep the deck wet enough for the 15-20 minutes dwell time and it dried out?

However, sanding will take off the white.

My question is whether sanding is enough and/or do I need to worry about this residue having an effect after staining with a semi-sold stain.

First picture - third board from left sanded

Second picture - up close of white

Thanks for any input.