Cleaner or brightener needed on new cedar pergola?

I'm building a cedar frame over a composite deck and large paver patio. I bought 6x6 rough cut lumber and I am just about finished sanding, so there's no glaze on it. I'm planning on using a colourless sealer but I'm wondering procedure and products are suggested. Some places say to wait till it's been installed 2-6 weeks to allow for lots of drying. Others say to use TSP or oxalic acid. Four of the uprights have already been installed on the deck, will these harsh cleaners likely wreck the capped composite? How about brighteners?

Any suggestions are greatly appreciated!