Cleaning
Cleaning hardwood is the same process as cleaning softer woods like PT. Start out with a Splash Test to determine whether or not the wood has ever been sealed. That means splash droplets on to the wood and see if they soak in. If they do, then you can clean with a percarbonate cleaner. If the droplets don't soak in, then I would suggest a Test Patch to determine what kind of sealer is on the wood. If the sealer turns out to be oil-based, then you can clean with a good caustic stripper. Wash with moderate pressure - 300 - 1000 PSI with a stripper, and 800 - 1500 with a percarb. Finish the job with a neutralizing (acidic) brightener. Those are the two steps.
Feel free to call and ask for more detail if you need it. Also, there are classes available that teach the chemistry and techniques of the wood restoration process.