TSP, bleach and water. 1qt bleach, 4oz TSP and 3qt's water. Mix it together, spray it on, let it dwell 15 minutes or so, and lightly powerwash.

 

I agree NC. I've used the cleaners from Ben Moore, Cabot and Pittsburgh. They all contain bleach. The naysayers will say (technically correctly) that bleach ruins the wood fibers. We have such heavy mildew, mold and occasionally moss here that nothing else but a bleach and water solution works. The ratio is determined by the severity, and TSP added if dirt or grease is suspected.
After letting it thoroughly dry, I give it a hard sanding. As far as I can tell it's back to new wood at that point. Never had a problem with this approach.

 

We strip every deck (with low pressure) unless we did the original finish and its a maintenance coat.

 

How many cycles before you strip a deck you are maintaining (if they follow your schedule). We tend to recommend after a full deck is done that in 2 years horizontals are done, then in 2 years everything is done, and then ??? No one follows our advice, so we have not been able to see the system we recommend to fruition at this point.