Black Stains

I would try and go to Lowe's or Home Depot and get their 10% SH, pump spray it on straight, brush it a little, wait about 5 minutes, rinse with hot water. It's something with their SH there that takes out fruit and berry stains like that.
 
Oak trees have a dark black tannin and the same principle is applied to deck and wood restoration. To neutralize the tannin stain use oxalic acid, clean with bleach and follow with oxalic acid. You will have a clean surface with out leaf or tannin stains. This is also the issue with composites where red oak was used in the composites and they too leave black spots when the wood content is exposed. Use a combination of bleach to clean and oxalic to neutralize.
 
Thank you. Makes sense. I had a pool that teaed on me from the oak droppings. Flat pool cage, rain, and a lot of leaves and acorns in the mix. The water looked like some one put tea bags in it for a day or so and then pulled them put. Got it cleared in 24 hours of filtering. Owner was happy. I will give the Home Depot or Lowe's SH a try with the oxcilic. Thanks to all for the help. I will update this as I go.
 
Where do you get oxcilic? I'm having trouble with leaf stains in gutters. Will it remove those as well?
 
Where do you get oxcilic? I'm having trouble with leaf stains in gutters. Will it remove those as well?

Lots of stuff has oxalic in it. AKA wood bleach. The home depot deck and fence cleaner is oxalic. I get mine from ebay. Just type in oxalic and there is a ton of suppliers. I think I paid $69 for 25 pounds shipped. Oh and to your leaf stain question in gutters. Never tried oxalic, butyl based cleaner takes care of those. Gutter zap. gutter grenade, purple degreaser. Just test area or you will be repainting. Don't mix too strong. usually have to use soft bristle brush and don't leave it on too long. rinse good.
 
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