By no means should this be considered the standard, we are not experts on wood but this works. Please leave suggestions in the comments if you have alternative methods and help out the community.
Before You Do Anything
Soak wood very well with fresh water….simple.
The Ratio & Method
Starting with a down stream, downstream straight 12.5 and surfactant and let dwell for a while while keeping an eye on it, making sure the mix does not dry on wood.
With very light pressure (25 degree tip) and a sweeping motion clean each board with at least 2 passes. Apply Oxalic Acid at the end to brighten the wood and bring back the natural PH levels in the wood.
For railings, we use a pump up sprayer, typically 1:1 ratio. It does not necessarily have to be that strong.
Wood cleaning is a tricky task to get down especially if you are trying to learn it all on your own. It will fur the wood bad. Some guys do not use SH at all, and only use wood stripper. We have not attempted that method yet.