Just so you know, I build decks and arbors for a living.
I have always discouraged the sanding of pressure treated wood, called PT wood. With the chemicals and junk in it, sanding does not work out too well. If the deck was redwood, cedar, teak, then that is different.
I have always subscribed to replacing the boards that become unsightly. A new board, at least in Texas, will turn the grey color in 6 weeks and less with City water sprayed on it regulary.
Now, Olympia and Behr are very inferior products in my opinion.
First Olympia deck cleaner is only water and bleach compound, you can do that. I have found that scouring powder and a stiff long handled brush is very good along with the bleach. One kills the algae, the other scrubs out the dirt. Then, a hose end nozzle or power washer will just jetison the debris away. BE SURE THAT THE WOOD IS THOROUGLY DRIED OUT BEFORE THE NEXT STEP. YOU DO NOT WANT TO TRAP WATER OR ALAE UNDER THE PAINT.
Second, Behr is topical and short lasting. Pay alittle more and find a product from the Flood Company, called CWF-UV. Sometimes sold in Sherwin Williams stores. This product soaks into the wood and penetrates as it stains. It comes in all colors and dries very quickly. It is water based and has to be hand painted or brushed or rolled on. This stuff sells for about $15 a gallon.
The first time you put this on, it will soak up allot and you will be using more than you anticipated. Then every Spring, I restain the decks and it takes about one half the amount as the first time.
This is undoubtly the best way to face lift a older deck. you will step back and say, man, why did we not do this sooner?
When you replace any boards, be sure to use galvanized or zinc coated fasteners. screw them in this time so that it is easier to remove the next time.